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ABSTRACT |
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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350 cells/µL (higher-CD4; N = 336) and HIV-negative subjects (N = 132) received multivitamins. Specimens were collected at baseline, 2 weeks, monthly, and at sick visits during 6 months of follow-up to compare changes in resistance, with higher-CD4 as referent. P. falciparum parasitemia incidence density was 16 and 156/100 person-years in lower-CD4 and higher-CD4, respectively (adjusted rate ratio [ARR] = 0.11; 95% confidence interval [CI] = 0.06–0.15; P < 0.001) and 97/100 person-years in HIV-negative subjects (ARR = 0.62; 95% CI = 0.44–0.86; P = 005). Incidence density of triple and quintuple dihydrofolate-reductase/dihydropteroate-synthetase mutations was 90% reduced in lower-CD4 compared with referent. Overall, cotrimoxazole non-susceptibility was high among isolated pneumococcus (92%) and E. coli (76%) and increased significantly in lower-CD4 subjects by Week 2 (P < 0.005). Daily cotrimoxazole prevented malaria and reduced incidence of antifolate-resistant P. falciparum but contributed to increased pneumococcus and commensal Escherichia coli resistance. |
INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Although recent international focus and funding have been directed toward increasing access to antiretrovirals in Africa, the vast majority of HIV-infected Africans still lack access to these life-saving drugs. Cotrimoxazole (CTX) or trimethoprim-sulfamethoxazole daily prophylaxis is a critical component of HIV care. Daily CTX is a low-cost regimen that has been shown to reduce morbidity and mortality in HIV-infected adults and children in sub-Saharan Africa.1–3 CTX prophylaxis reduces the incidence of illness caused by bacterial and parasitic agents, including malaria, pneumonia, and diarrhea in areas with both low and high prevalence of CTX-resistant bacteria.1–3 In addition, CTX prophylaxis slows HIV progression3 and reduces morbidity and mortality among HIV-negative family members.1,4 However, concerns remain about the consequences of widespread CTX prophylaxis, specifically whether such use would promote corresponding population-level resistance with resultant loss of the utility of CTX to treat life-threatening bacterial infections and the loss of sulfadoxine pyrimethamine (SP) to treat malaria caused by Plasmodium falciparum.2,5–9
Although many countries have changed their first-line an-timalarial treatment to artemisinin-containing combination therapies, SP continues to be used for treatment of uncomplicated malaria, usually as a component of combination therapy or as monotherapy for intermittent preventive treatment of malaria in pregnancy (IPTp) and in infants (IPTi).10 SP inhibits two critical enzymes in the P. falciparum folic acid biosynthetic pathway: pyrimethamine inhibits dihydrofolate reductase (DHFR), whereas sulfadoxine inhibits dihydropteroate synthetase (DHPS). Mutations in the DHFR and DHPS genes have been associated with SP resistance.11–15 The presence of triple mutations in the DHFR gene have been correlated with a high level of clinical resistance to antifolate drugs in Africa. The addition of specific DHPS mutations, creating a quintuple mutation, increases resistance to SP and another antifolate antimalarial drug, chlorproguanil dapsone.16
We conducted a prospective study to assess whether the use of daily CTX resulted in significant changes in antifolate and CTX resistance among common organisms. We measured the change in prevalence of antifolate-resistant P. falciparum malaria by identifying mutations at the DHFR and DHPS alleles. We measured changes in the prevalence of CTX- and penicillin-resistant naso- or oro-pharyngeal Streptococcus pneumoniae (pneumococcus) as a surrogate for invasive disease.17–21 Like other investigators in resource-poor settings, we measured the prevalence of CTX-resistant commensal Escherichia coli as a marker for CTX-resistance among other pathogenic Enterobacteriaceae (e.g., Shigella, Salmonella). Because of the rapid plasmid-mediated transfer of CTX resistance between fecal E. coli and other Enterobacteriaceae, the prevalence of fecal E. coli resistance to CTX could reflect similar resistance patterns in pathogenic Enterobacteriaceae.22
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Study site. The study was conducted at the KEMRI/CDC Clinical Research Center at the Nyanza Provincial General Hospital in Kisumu city between May 2002 and December 2003. HIV prevalence is high in Kisumu; 20% of men and 30% of women 15–49 years of age are HIV infected.23 At the initiation of this study, a single HIV voluntary counseling and testing site had recently opened in Kisumu, no centers had been established to provide medical care for HIV-infected persons and daily CTX for prophylaxis of opportunistic infections (OI) among HIV-infected persons was not yet recommended by the Kenyan Ministry of Health. Although antiretroviral access has increased in Kenya during the past 3 years, antiretrovirals were poorly accessible in Kenya throughout the study period.
Nyanza Province has perennial malaria transmission, with > 98% of infections caused by P. falciparum. Residents living in the periurban area of Kisumu receive up to 400 infectious bites per person per year.24 At the time of this study, SP was the first-line therapy for uncomplicated malaria and for IPTp and was widely available in health facilities and in the community.
In addition to malaria, acute respiratory infections and di-arrheal diseases are common illnesses and leading causes of childhood death in Nyanza Province.25 CTX is the first-line antibiotic for empiric treatment of respiratory infections. Although not officially recommended by the Ministry of Health, CTX is also commonly prescribed for treatment of acute bloody or non-bloody diarrhea.26
Design. We conducted a prospective, open-label, non-randomized cohort trial to compare the incidence density of antifolate-resistant P. falciparum and the prevalence of CTX-resistant nasopharyngeal S. pneumoniae and gastrointestinal E. coli among HIV-infected persons receiving daily CTX for OI prophylaxis with HIV-infected persons not receiving daily CTX. We aimed to enroll between 680 and 1,380 HIV-infected persons, depending on baseline prevalence of DHFR and DHPS mutations to measure a 3-fold difference in the incidence density of antifolate markers of resistance among HIV-infected subjects taking daily CTX and those not taking daily CTX with 80% power at the 95% confidence level. We aimed to enroll ~100 HIV-negative adults to reduce any stigma associated with enrollment in the study and to measure changes in the same resistance markers.
Eligible subjects 15 years of age and older, who agreed to HIV testing, were not severely ill nor in the first trimester of pregnancy, and who were not taking daily antibiotics for treatment of a chronic illness (excluding tuberculosis) were recruited into the study from local home-based care organizations. Home-based care organizations typically provided emotional support and nursing care to community members presumed to be HIV-infected, but no medications. Subjects were also recruited from the sole voluntary HIV counseling and testing site that had been established in Kisumu several months before the initiation of our study. At the initial screening visit, eligible subjects underwent HIV pre- and post-test counseling according to national guidelines and were tested for HIV infection, and their CD4 cell count was measured. All consenting eligible HIV-infected subjects and a systematic sample of eligible HIV-negative subjects were asked to return for enrollment. Subjects who began antibiotics or antimalarial drugs after screening were not enrolled until at least 3 full days after completing the antimicrobial course.
At the enrollment or baseline visit, demographic, socioeconomic, and risk factor data were collected. The study clinician performed a medical history and physical examination. A blood sample was taken to measure leukocyte count, hemoglobin, and malaria parasitemia and for genotyping at the P. falciparum DHFR and DHPS alleles. Naso- and oropharyngeal swabs, stool samples, and rectal swabs were collected.
Subjects were assigned to study arms according to HIV status and CD4 cell count at screening. HIV-infected subjects presenting with CD4 cell count < 350 cells/µL (lower-CD4) were provided daily CTX (800 mg sulfamethoxazole, 160 mg trimethoprim) as a single tablet per day. HIV-infected subjects with CD4 cell count 350 cells/µL (higher-CD4) and HIV-negative subjects (HIV-negative) were provided a daily multivitamin. The multivitamins provided contained no more than the recommended daily allowance of each vitamin and were provided so that clients in each arm received a study drug at scheduled visits. This was done to reduce identification by other participants of those who were HIV infected. Multivitamins were selected as the drug for the non-intervention arms before reports that higher doses of multi-vitamins reduce progression of HIV disease.27
The threshold of CD4 count < 350 cells/µL for initiation of CTX prophylaxis was selected after consultation with HIV experts including members of the Kenyan Ministry of Health and was based on findings from the randomized controlled trial of CTX prophylaxis conducted in Abidjan, which showed a mortality benefit for subjects with CD4 cell counts < 350 cells/µL2.
All subjects were asked to return to the clinic for scheduled visits 2 weeks after beginning study drugs and every 4 weeks thereafter for a total of six monthly visits. Subjects were also asked to return for assessment and treatment any time they became ill between scheduled visits. To increase likelihood of adherence with this request, transport reimbursement was provided for all visits. At all visits, a blood sample was collected for malaria smears, hemoglobin, and parasite genotyping. At the initial, Week 2 and Months 2, 4, and 6 visits, naso-and oro-pharyngeal swabs were collected for pneumococcus isolation and antimicrobial sensitivity testing. A stool sample or rectal swab was collected for E. coli antimicrobial sensitivity testing at Months 2, 4, and 6 visits; a Week 2 sample collection was added in March 2003. Collection of routine stool specimens stopped in August 2003, when sufficient sample size was achieved. At every visit, subjects were examined by a study nurse or clinician and asked questions about recent illness, health facility visits, hospitalizations, antimicrobial use since the last visit, and adherence to study drug. Pill counts were conducted to verify reported adherence. Discrepancies in pill counts and reported adherence were probed and recorded adherence was adjusted accordingly. Study drug supplies were replenished, such that sufficient pills were provided to last to the next follow-up visit plus six additional pills. Subjects who presented late for follow-up visits and therefore ran out of study drug were considered to have missed doses of study drug.
At any visit, subjects with either P. falciparum infection with measured or reported fever or P. falciparum infection with parasite density 400 parasites/µL regardless of fever, were diagnosed with clinical malaria and provided SP for treatment of malaria according to national guidelines at the time of the study The cutoff of 400 parasites/µL was selected as a reasonable threshold based on earlier epidemiologic studies in children in the same area.28
Subjects treated with SP were asked to return to the clinic 7 and 14 days after treatment or any time if their condition worsened for a repeat malaria blood smear. Those who failed SP were treated with artemether-lumefantrine or quinine. Daily CTX was not withheld when SP was provided.
Laboratory tests. HIV testing. HIV testing was done using Unigold (Abbott Laboratories, Tokyo, Japan) and Determine (Trinity Biotech, Bray, Ireland) rapid HIV tests, run in parallel. Discordant results were resolved using the Capillus (Cambridge Diagnostics, Wiclow, Ireland) test according to Kenyan national guidelines.
Malaria smears. Giemsa-stained thick and thin blood smears were prepared from finger stick blood samples. Parasite densities were estimated by counting the number of asexual parasites per 300 white blood cells. Measured leukocyte counts were used to calculate densities. Blood smears were examined independently by two microscopists; discordant results were resolved based on a reading by a third independent microscopist.
Plasmodium falciparum molecular analysis. All P. falciparum infections identified by light microscopic examination of thick and thin blood smears, regardless of parasite density, were genotyped for mutations at codons 50, 51, 59, and 108 in DHFR and at codons 437 and 540 in DHPS by restriction fragment length polymorphism (RFLP). When attempts to genotype by RFLP method failed, we used pyrosequencing to complete genotyping. All samples with DHFR Leu164 mutation by RFLP were confirmed using direct sequencing and/or pyrosequencing as previously described.29,30
We designated specimens with two mutations isolated at DHFR codons 108 and 51 or 59 a double mutation, those with mutations at codons 108, 51, and 59 a triple mutation, and a triple DHFR mutation with mutations at codons DHPS 437 and 540 a quintuple mutation.
Pneumococcus isolation and analysis.
Naso- and oro-pharyngeal swabs were immediately placed in a culture media consisting of skim milk, glycerol, and glucose, and after transport, were frozen at –70°C. Swabs were plated onto defibrinated sheep’s blood agar with 5% gentamicin and incubated at 37°C for 24–48 hours. Pneumococcal colonies were identified by morphology and optochin susceptibility. Subcultures of pneumococcal colonies were plated onto Mueller-Hinton sheep’s blood agar and tested for susceptibility to CTX and penicillin using CTX and oxacillin disks. Isolates underwent minimum inhibitory concentration (MIC) testing using the broth microdilution technique for CTX and penicillin according to guidelines established by the National Committee for Clinical Laboratory Standards (NCCLS).31 Pneumococcus non-susceptibility to CTX and penicillin was defined as MIC of 1 µg/mL.
Enteric specimens. Swabs of fresh whole stool or rectal swabs were placed in Cary-Blair media, transported cold (4°C) to the CDC/KEMRI laboratory, and cultured for E. coli by plating on MacConkey agar and incubating for 24 hours at 37°C. One E. coli colony was selected from each plate and subcultured and then tested for susceptibility to CTX by the disc diffusion method per NCCLS guidelines.31
Other tests. All women of childbearing age not visibly pregnant had a rapid urine pregnancy test performed at enrollment. Hemoglobin was measured using Hemocue machines (Hemocue, Angelholm, Sweden).
Data analysis and statistical testing. Monthly visits were scheduled at 4-week intervals, giving a total follow-up time of 24 weeks. Those presenting late for scheduled visits were seen, and data were included in the analysis. In determining malaria incidence density, subjects who were treated with SP were not considered to be at risk for malaria for 28 days after SP treatment. Subjects with a positive malaria smear with low parasitemia, who did not receive treatment, were not considered to be at risk for malaria until after they had a subsequent blood smear negative for malaria parasitemia. All visits, both scheduled and sick visits, were used to calculate incidence density of P. falciparum parasitemia and antifolate resistance. Because baseline measurements differed between study arms, we compared the change in resistance from baseline to follow-up visits for each study arm for measurements of anti-folate resistance, pneumococcus isolate non-susceptibility, carriage of non-susceptible pneumococcus, and E. coli resistance.
Categorical variables were compared with 
2 or Fisher exact tests and continuous variables with rank-sum and t-tests. Kaplan-Meier survival plots were used to describe time-to-first-malaria-infection, right censored at the subject’s last study visit. Study arm comparisons were made with the log-rank test.
We used Poisson regression to model changes in P. falciparum resistance from baseline through follow-up. Follow-up time was truncated at the last study date or first malaria infection date for the model of first or only malaria infection and at the last study date only for the model of multiple malaria infections. Follow-up time was decreased by 28 days for subjects who received SP. To model incidence of anti-folate resistance markers, we used logistic regression models (generalized estimating equations with a logit link function; SAS 9.1; SAS Institute, Cary, NC) to account for correlated observations. Initially we adjusted for housing type, parasitemia at baseline, seasonality (high transmission versus low transmission), ITN use, prior antimalarial use, and hemoglobin at baseline. We removed seasonality, prior antimalarial use, and baseline hemoglobin from the model because they were non-significant. Although ITN use also was non-significant, we retained this variable in the model.
We modeled change in pneumococcus and E. coli resistance with logistic regression models using generalized estimating equations. We adjusted for housing type, seasonality (rainy versus dry), recent antibiotic use, and recent antifolate use for pneumococcus-specific data. Housing type and recent antibiotic use were significant, and seasonality approached significance. In the model for diarrhea-specific data, we adjusted for housing type, seasonality (rainy versus dry), recent antibiotic or antifolate use, and diarrhea during the prior 24 hours. Recent antifolate and antibiotic use was significant.
When analyzing P. falciparum resistance markers, we compared the incidence density at individual codons, triple mutations, and quintuple mutations. We calculated 95% confidence limits by adding a false record with small weight (0.05) to avoid the problem of zero counts in some cells. We classified mutations as triple and quintuple pure, indicating single clonal infections, and triple and quintuple mixed, indicating polyclonal infections, as described by Kublin and others.16 Bonferroni correction was used when multiple comparisons were made.
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RESULTS |
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350 (higher-CD4) received a daily multivitamin, whereas 692 subjects with CD4 cell count < 350 (lower-CD4) received daily CTX. The study profile is shown in Figure 1
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. Lower-CD4 subjects were older than higher-CD4 subjects (referent). HIV-negative subjects had higher median hemoglobin, whereas lower-CD4 subjects had lower median hemoglobin compared with the referent. Malaria parasitemia prevalence was lower in lower-CD4 than higher-CD4 subjects; this difference remained significant after controlling for hemoglobin, ITN use, prior antimalarial use, and housing type (adjusted rate ratio [RR] = 0.53; 95% confidence interval [CI] = 0.34 – 0.82; P < 0.025). Subjects in all study arms reported high recent antibiotic and antimalarial use, although HIV-negative subjects reported lower use than the referent. Lower-CD4 subjects had higher antibiotic and antimalarial use in the week before enrollment compared with the referent.
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Eleven subjects discontinued the study because of a drug reaction: all in the lower-CD4 arm. Two subjects experienced a severe adverse reaction to CTX, both with blistering rash that resolved uneventfully after discontinuation of CTX; the other nine experienced mild rash. Other reasons for not completing 6 months of follow-up did not differ by study arm. Drug adherence was high; 85% of subjects in all study arms reported missing no doses of study drugs. A total of 7 subjects in the HIV-negative arm and 37 in the higher CD4 arm reported taking at least one course of CTX for treatment of illness during the follow-up period. There was no difference in number of sick visits by study arm, with an average of 2.8, 3.0, and 3.2 per person-year in the HIV-negative, higher-CD4, and lower-CD4 arms, respectively (P > 0.05 for HIV-negative and for lower-CD4 compared with reference).
CTX and parasitemia.
Lower-CD4 subjects had an estimated 90% reduction in incidence density of first or only infection with P. falciparum parasitemia compared with higher-CD4 subjects (Figure 2; Table 2) and a similar reduction in incidence density for all episodes of P. falciparum parasitemia. This protective effect of 89–90% against P. falciparum infection in the CTX-administered group remained after adjusting for prior P. falciparum parasitemia, SP use, ITN use, and housing type in Poisson regression models (P < 0.001). HIV-negative subjects had a significant (38%) reduction in all episodes of P. falciparum parasitemia (P < 0.018 adjusted) compared with referent. Compared with lower-CD4 subjects who reported missing no study drug in the prior month, lower-CD4 subjects who missed any or all doses of CTX in the prior month were at a 3-fold (RR = 3.0, 95% CI = 1.20–7.06 adjusted for correlated data) and 11-fold (RR = 10.7, 95% CI = 3.46–33.17 adjusted for correlated data) increased risk of parasitemia during the subsequent follow-up visit, respectively.
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The prevalence of triple and quintuple mutations generally increased in all study arms, but there was no significant increase among lower-CD4 subjects compared with the higher-CD4 subjects (Table 3). Notably, because of the low parasite incidence density among lower-CD4 subjects, the incidence density of triple and quintuple mutant DHFR/DHPS genotypes in lower-CD4 subjects was significantly lower than in higher-CD4 subjects (Table 4).
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400 parasites/µL regardless of fever), 0/8 (0%), 2/31 (6%), and 2/18 (11%) of subjects treated with SP in the HIV-negative, lower-CD4, and higher-CD4 arms, respectively, returned with P. falciparum parasitemia by Day 14. Among subjects who presented with clinical malaria during follow-up, after beginning study drug, 0/11 (0%) HIV-negative, 2/14 (14%) lower-CD4, and 2/67 (3%) higher-CD4 subjects had parasitemia detected by Day 14.
CTX non-susceptible pneumococcus.
A total of 25/129 (19%), 241/687 (35%), and 112/334 (34%) of HIV-negative, lower-CD4, and higher-CD4 subjects, respectively, had pneumococcus isolated at baseline. The percentage of isolates that were CTX non-susceptible was high in all study arms (range: 76–93%) at baseline (Figure 3) and increased significantly in lower-CD4 subjects, with 223/241 (93%) isolates resistant at baseline and 196/196 (100%) isolates resistant 2 weeks later (P = 0.005). The prevalence of non-susceptible isolates remained high in lower-CD4 subjects at month 6, when 99% of 164 isolates were found to be non-susceptible to CTX.
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At baseline, 56%, 85%, and 76% of pneumococcal isolates were non-susceptible to penicillin in HIV-negative, lower-CD4, and higher-CD4 subjects, respectively. The prevalence of penicillin non-susceptible isolates increased significantly in only HIV-negative subjects to 92% at 6 months (P = 0.035).
Escherichia coli resistance. Commensal E. coli was isolated from 100% of samples taken at baseline and during follow-up. Prevalence of CTX-resistant E. coli was high in all study arms at baseline: 70% (92/132), 79% (542/688), and 74% (248/333) in HIV-negative, lower-CD4, and higher-CD4 subjects, respectively, but significantly increased only among lower-CD4 subjects, reaching 98% (172/176) by Week 2 (P < 0.0001). CTX resistance remained high through Month 6 (96% [277/ 290] of isolates). The increase in CTX-resistant E. coli was significantly greater among lower-CD4 subjects compared with the referent (P < 0.01 adjusted).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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In this malaria-endemic area, we found that daily CTX significantly reduced malaria incidence, with a protective efficacy of 89%. Because of the decreased incidence of malaria, daily CTX resulted in an almost 90% reduction in molecular markers of high-level antifolate resistance compared with HIV-infected subjects not taking daily CTX. Thus, in this setting, it seems unlikely that daily CTX use will contribute significantly to the loss of antifolate antimalarials for prevention or treatment of P. falciparum malaria. These findings support recommendations to provide CTX for HIV-infected persons in Africa.
Although SP monotherapy is no longer recommended as first-line treatment of malaria in most African countries, it still frequently is used as monotherapy,32 as well as a component of combination therapy, remains the only recommended drug for IPTp and soon may be recommended for IPTi. Our finding that daily CTX use does not select for antifolate-resistant P. falciparum provides valuable reassurance to malaria control policy makers and managers who govern in areas where HIV and malaria endemicity overlap; SP use can continue in recommended capacities, even as daily CTX use by HIV-infected persons becomes widespread.
We were underpowered to measure the effectiveness of SP for treatment of clinical malaria in study subjects. There may have been a trend toward increased SP failure among lower-CD4 subjects; however, numbers were small and should be considered with caution. Nonetheless, effectiveness of SP remained > 85% in all study arms.
Importantly, taking daily CTX prevented malaria parasitemia despite high levels of triple and quintuple DHFR/DHPS mutations. This finding is particularly surprising when one considers that the subjects assigned to take daily CTX were the most immunosuppressed. Most likely, CTX adequately prevented malaria despite high prevalence of antifolate-resistant genotypes because of pre-existing levels of malaria-specific acquired immunity among this adult population living in an area of high malaria endemicity. Pre-existing acquired immunity likely also explains the low frequency of SP failure in these adults compared with children, in whom 26% younger than 5 years of age in this region fail SP treatment.33 These findings underscore the complex nature of immunity and the limitations of in vitro measures of resistance, especially when extrapolating to the clinical effects of daily prophylaxis. Likewise, extrapolation of measures of pneumococcus and E. coli resistance to CTX prophylactic efficacy may not be straightforward. Prior studies in Uganda, Zambia, and Malawi have shown reduced morbidity and mortality among those taking daily CTX despite high resistance levels among pathogens targeted by the intervention.3,9,34 In Zambia, in vitro CTX resistance among common pathogens was estimated between 60% and 80%, yet daily CTX decreased mortality in HIV-infected children.
We found that daily CTX resulted in relatively higher prevalence of non-susceptible pneumococcus carriage, with the unexpected finding that overall pneumococcus carriage declined among those in the higher-CD4 and HIV-negative arms while remaining stable in the lower-CD4 arm. We cannot definitively explain this decline; however, subjects in our study received regular medical care, including antibiotic prescriptions when needed, and those in the higher-CD4 and HIV-negative arms received a multivitamin. It may be that subjects with a more intact immune system responded to good health care and occasional antibiotic therapy by resolving pneumococcus carriage, whereas those who were immunosuppressed were unable to clear carriage.
The prevalence of penicillin non-susceptible pneumococcus isolates was also high at baseline and increased only among HIV-negative subjects, who had the lowest baseline prevalence of penicillin non-susceptible isolates. Notably, HIV-negative subjects had less recent antibiotic use at baseline compared with the other study arms, and this likely accounts for the lower proportion of non-susceptible isolates at baseline. Again, non-susceptible isolates reached the prevalence of the other two study arms during follow-up.
In Kenya, the rise in non-susceptible pneumococcus, similar to the rise observed in resistant E. coli carriage, may be statistically significant but not clinically significant. For both bacteria, the prevalence of in vivo CTX resistance was very high before the study drug was begun. Based on these findings, the Ministry of Health might consider alternatives to CTX, such as amoxicillin, for presumptive treatment of non-severe lower respiratory infections. They might also emphasize adherence to current guidelines that propose nalidixic acid, not CTX, for the treatment of bloody diarrhea and shigella.35 However, the implication for countries with lower levels of CTX resistance merits serious consideration, especially considering the rapid rise in CTX resistance documented in our study.
Because daily CTX was shown to be an efficacious intervention before this study, we were unable to randomize subjects or blind treatment arms. We have been unable to explain the difference in malaria parasitemia among study arms at baseline, specifically the unexpected finding that P. falciparum prevalence was reduced among those with lower CD4 cell counts, even after controlling for prior antimalarial use and indicators of P. falciparum exposure, such as housing type and ITN use. The primary malaria-transmitting vectors in Nyanza Province, Anopheles gambiae and Anopheles funestus,36 bite primarily late at night, when people are asleep indoors. Traditional and semi-permanent houses have open eaves for ventilation, and allow unobstructed movement of mosquitoes in and out of houses; thus, lack of movement out of doors at night among those in the lower-CD4 arm would not necessarily reduce exposure to anopheline mosquito bites. Additionally, there was no difference between study arms in ITN use to explain decreased exposure. We do find more antimalarial use in the week preceding enrollment among those in the lower-CD4 arm, which is not unexpected; in Kenya, reported fever is typically diagnosed and treated as malaria without blood smear confirmation. Subjects were informed at screening that enrollment would be deferred until at least 3 days after completion of any antimalarial drugs, and it may be that recent antimalarial use was therefore under-reported.
Although subjects in the lower-CD4 arm had lower P. falciparum prevalence at baseline, they did not have lower geometric mean parasite density compared with the reference. This suggests that lower parasite prevalence is likely caused by unmeasured factors, such as recent antimalarial use not reported, and is not caused by an immunologic difference among those in the lower CD4 arm, which resulted in less malaria parasitemia. This assumption is further supported by the finding that missing doses of daily CTX significantly increased risk for subsequent malaria infection during the follow-up period, with an 11-fold increased risk if all CTX doses were missed in the prior month.
Our study had other limitations, including a relatively short study period, with ~24 weeks follow-up. As CTX use becomes widespread, the effectiveness in preventing malaria and preventing breakthrough parasitemia with highly resistant genomes may wane and should be monitored. We also experienced a moderately high loss to follow-up; 32% of subjects failed to make the Month 6 visits. This could have impacted our results; however, we are reassured that there were no differences in baseline characteristics within study arms between those who did and did not complete the Month 6 visit.
To study resistance in pneumococcus, we used nasopharyngeal pneumococcus as a surrogate for invasive disease. Although invasive disease is generally caused by strains that are carried in the nasopharynx, certain serotypes tend to be more or less invasive.17–19 Because antibiotic resistance in pneumococcus is confined to a handful of serotypes, which tend to be the serotypes that predominate in carriage, it is possible that the evaluation of carried pneumococci for this study might slightly overestimate the impact of CTX prophylaxis in non-susceptibility among invasive pneumococci.
Finally, when looking at enteric organisms, we measured change in resistance in commensal E. coli and not enteric pathogens. Although it would have been more informative to have measured the change in diarrheagenic E. coli or other bacterial enteric pathogens, the relative rarity of these pathogens would have necessitated a much larger sample size. However, there is a high degree of rapid plasmid-mediated transfer of CTX resistance between fecal E. coli and Salmonella, as well as other Enterobacteriaceae, and thus, commensal E. coli can be used as a reasonable surrogate to measure the development of resistance in bacterial enteric pathogens.37–39
We have shown that daily CTX did not result in increased P. falciparum antifolate resistance; rather, daily CTX was associated with a reduced incidence of malaria and antifolate-resistant genotypes compared with HIV-infected individuals not taking daily CTX. In contrast, daily CTX increased carriage of non-susceptible pneumococci and CTX-resistant E. coli and may accelerate the development of CTX resistance among respiratory and diarrheal pathogens, especially in areas with lower baseline CTX resistance. Our findings add essential information and further support the widespread adoption of daily CTX prophylaxis for HIV-infected individuals in Africa. As CTX prophylaxis is adopted into national health programs across Africa, surveillance systems should be established to monitor for increasing incidence of breakthrough malaria infection and to look for increased CTX resistance among respiratory and diarrheal disease pathogens. Ministries of Health adopting daily CTX prophylaxis should introduce strategies to maintain good adherence to daily CTX and should begin to identify alternative treatments other than CTX for respiratory and enteric diseases.
Received November 23, 2007. Accepted for publication May 30, 2008.
Acknowledgments: We thank the subjects who participated in this study, the CTX clinical staff who provided caring support to the subjects, including Monica Aluoch Ochieng, Mary Owino, Ida Ouma, Agnes Owiti, Grace Otom, and Mary Caesar, the scientific and laboratory team including Ananias Escalante and Venkatachalam Udhayakumar, who provided oversight and technical expertise for the molecular resistance laboratory work, and Cheryl Bopp, Richard R. Facklam, Mary Omwalo, Geoffrey Jagero, Dickens Olang, Lata Kumar, and Ira Goldman. We also thank Carolyn Wright and Kathleen Wannemuehler who contributed to data management and cleaning, Anne Schuchat for technical guidance, and John Vulule for support.
Financial support: Funding was provided for by the Opportunistic Infections Working Group, Centers for Disease Control and Prevention, and the Antimicrobial Resistance Working Group, Centers for Disease Control and Prevention. AAE was supported by NIH Grant R01 GM60740.
Disclosure: The authors do not have a commercial or other association that might pose a conflict of interest. The funding organizations had no role in the design and conduct of the study; in the collection, analysis and interpretation of the data; or in the preparation, review, or approval of the manuscript.
* Address correspondence to Mary J. Hamel, Unit 64112, APO 09831. E-mail: mhamel{at}ke.cdc.gov 
Authors’ addresses: Mary J. Hamel, KEMRI/CDC Research Station, Unit 64112, APO 09831, Tel: 254-722-772-616, Fax: 254-57-20-22981, E-mail: mhamel{at}ke.cdc.gov. Carolyn Greene, Bureau of Public Health Training, NYC Department of Health and Mental Hygiene, 2 Lafayette Street, New York, NY 10007. Tom Chiller, John Williamson, Barbara Marston, John T. Brooks, Amanda Poe, Zhiyong Zhou, Ya Ping Shi, Eric Mintz, and Laurence Slutsker, Center for Disease Control and Prevention, 1600 Clifton Road, NE, Atlanta, GA 30333. Peter Ouma, Kephas Otieno, and Benjamin Ochieng, Box 1678, Kisuma, Kenya. Christina Polyak, 1513 Belt Street, Baltimore, MD 21202.
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| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
