Enteric infections pose a major health concern for low-resource populations worldwide, especially in young children, for whom diarrheal disease is a leading cause of mortality.1 There is an increasing number of persons displaced by wars and natural disasters around the world, with over 65 million displaced persons reported in 2015.2 Persons living in camps for refugees and internally displaced persons (IDPs) may have an increased risk for diarrheal diseases because of crowded living conditions and inadequate access to safe water and sanitation.3,4 This poses risk for pathogen spread among those living and working in camps, as demonstrated by a recent report of Shigella infections among refugees and staff in European transit centers.5
Studies have demonstrated a high burden of asymptomatic enteropathogen carriage among persons in low-income countries, particular in young children,6 although there are few data in adults. Asymptomatic or subclinical carriage of pathogens may contribute to spread of diarrheal diseases, especially for microbes that require a low infectious dose, such as Shigella spp.7 Little is known regarding the burden of enteropathogen carriage in IDP camps, many of which may have an environment conducive to the spread of enteric pathogens and a large susceptible population, including many children. Recent advances in technology have enabled probing of enteropathogen prevalence among populations using culture-independent methods.6,8,9 Our objective was to explore the distribution of enteropathogen carriage of persons living in an IDP camp in South Sudan.
As part of a mass vaccination campaign in an IDP camp in Juba, South Sudan, we obtained stool samples from a convenience sample of 88 healthy vaccine recipients with no obvious or self-reported signs of acute diarrheal illness within the week before their first dose of a killed whole cell oral cholera vaccine.10 We stored and shipped stool samples at −80°C and dry ice. Stool was diluted in PBS at 1:10 ratio and extracted on the Chemagen II (Perkin Elmer, Baesweiler, Germany) using a 2× Blood Lysis kit. Multiplex real-time polymerase chain reaction was performed to detect a panel of 20 bacterial, viral, and protozoal targets (Table 1) using a validated laboratory-developed test (ARUP Laboratories, Salt Lake City, UT). The study protocol was reviewed and approved by the ethical review committee of the South Sudan Ministry of Health and the institutional review boards of Johns Hopkins Bloomberg School for Public Health and the University of Utah.
Enteropathogens detected in fecal samples from asymptomatic subjects living in an internally displaced persons camp in South Sudan
| 1–5 yrs (N = 8) | 6–17 yrs (N = 27) | 18+ yrs (N = 53) | Total (N = 88) | |
|---|---|---|---|---|
| Shigella spp./EIEC | 2 | 1 | 9 | 12 |
| Dientamoeba fragilis | 1 | 7 | 3 | 11 |
| Norovirus G1/G2 | 2 | 2 | 6 | 10 |
| Shiga toxin E. coli (STEC) | 0 | 2 | 6 | 8 |
| Salmonella spp. | 1 | 4 | 1 | 6 |
| Campylobacter jejuni/coli | 0 | 3 | 2 | 5 |
| Giardia spp. | 1 | 1 | 2 | 4 |
| Cryptosporidium spp. | 0 | 0 | 2 | 2 |
| Adenovirus | 0 | 1 | 0 | 1 |
| Other Campylobacter spp.* | 0 | 0 | 1 | 1 |
| Sapovirus | 0 | 0 | 1 | 1 |
| Astrovirus | 0 | 0 | 0 | 0 |
| Campylobacter upsaliensis | 0 | 0 | 0 | 0 |
| Cyclospora spp. | 0 | 0 | 0 | 0 |
| Entamoeba histolytica | 0 | 0 | 0 | 0 |
| Hepatitis E virus | 0 | 0 | 0 | 0 |
| Rotavirus | 0 | 0 | 0 | 0 |
| Vibrio cholerae | 0 | 0 | 0 | 0 |
| ≥ 1 pathogens | 4 (50%) | 13 (48%) | 23 (43%) | 40 (45%) |
| ≥ 2 pathogens | 2 (25%) | 7 (26%) | 10 (19%) | 19 (22%) |
| ≥ 3 pathogens | 1 (13%) | 1 (4%) | 3 (6%) | 5 (6%) |
EIEC = enteroinvasive Escherichia coli.
Campylobacter ureolyticus, Campylobacter lari, Campylobacter hyointestinalis.
RESULTS
We found a high prevalence of enteropathogen carriage among the 88 participants, across all age groups (Table 1). Overall, 45% (40/88) of subjects had at least one pathogen detected in stool, with 22% (19/88) having two or more. Among those aged 1–5 years (N = 8), 6–17 years (N = 27), and 18–60 years (N = 53), 50%, 48%, and 43% of subjects, respectively, had at least one enteropathogen detected in stool. The most commonly detected pathogens were Shigella spp. or enteroinvasive Escherichia coli (EIEC) in 14% (12/88), Dientamoeba fragilis in 13% (11/88), norovirus (G1/G2) in 11% (10/88), and Shiga toxin–producing Escherichia coli in 9% (8/88). We did not find any differences in the prevalence of enteropathogen carriage between age groups or geographic state of origin.
The most prevalent enteropathogens found in our study were Shigella spp. or EIEC. Globally, Shigella is a leading cause of moderate to severe diarrhea in young children.11 The parasite Shigella spreads easily from person to person, particularly in densely populated or overcrowded conditions,12 including daycare centers13 and displaced person camps.4,5 This ease of spread may be associated with the low inoculum size necessary to cause infection.7 Furthermore, in a camp that draws IDPs from different, sometimes far away, regions, persons may encounter different serotypes than the ones for which they have immunity. Altogether, the high rates of Shigella carriage is highly concerning given the crowded living conditions of an IDP camp and the potential introduction of novel serotypes to nonimmune populations.
Despite decreasing diarrhea-related deaths over the past decade,1 diarrheal diseases are still among the top three causes of under-5 child mortality in sub-Saharan Africa and in 2013 were responsible for an estimated 520,000 deaths globally for those under the age of 5.1 A recent report demonstrated that young children accounted for the largest burden of infections and deaths during a Shigella outbreak in an IDP camp in Papua New Guinea.5 Little is known about the asymptomatic carriage of Shigella in adults and its impact on children living in their proximity. Regardless of the pathogen type, the contribution of enteropathogen carriage to the transmission of diarrheal diseases among displaced persons living in camps is unknown. Asymptomatic carriers are a potential source for transmission of enteric pathogens in other settings,14–16 and prospective cohort studies with microbial strain typing are needed given the unique context of a displaced persons camp. A better understanding of the transmission patterns and the importance of asymptomatic carriage could certainly improve the public health interventions and decrease the diarrheal diseases burden in highly vulnerable populations.
Our study has several limitations. We used a convenience sample from a single IDP camp without controlling for household or regional clustering, so generalizability is limited. Although no mass–treatments had been reported at the camp, we did not collect data on historical antibiotic use among these individuals, and the lack of diarrheal symptoms were self-reported. Third, we used only molecular detection of pathogens, and thus, serotypes and antibiotic susceptibility patterns were not examined, and no isolates were available to further distinguish Shigella from EIEC, which causes a syndrome that is clinically indistinguishable from shigellosis. Despite these limitations, we report a high prevalence of asymptomatic Shigella spp. or EIEC carriage among IDPs in a camp in South Sudan. With the rise in displaced persons worldwide, the potential for such carriage to contribute to disease transmission needs further examination.
Acknowledgments:
We would like to thank the study staff, participants, community leaders in the UN House PoC, staff at the WHO Juba Country Office, and International Medical Corps staff. This work was sponsored by The National Institute of Health (K08 AI100923 grant to D. T. L.), The Bill & Melinda Gates Foundation (OPP1089243 to A. S. A., Delivering Oral Vaccine Effectively (DOVE) Project, OPP153556 to D. A. S., F. J. L., A. S. A., and OPP 1089248 to WHO), and Margaret A Cargill Foundation grants to the WHO.
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