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    Viral isolation rate of serologically confirmed acute dengue infections during study period.

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    Armed Forces Research Institued of Medical Sciences serologically confirmed dengue cases and ministry of public health reported incidence for Bangkok, Thailand

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    Seasonal occurrence of serologically condirmed dengue virus infection and dengue serotypes at the Queen Sirikit National Institute for Child Health from 1973–1999.

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    Percentage of primary dengue of all diagnosed dengue cases by year

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    Age distribution of infants with dengue hemorrhagic fever and fatal dengue

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SEROTYPE-SPECIFIC DENGUE VIRUS CIRCULATION AND DENGUE DISEASE IN BANGKOK, THAILAND FROM 1973 TO 1999

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  • 1 Department of Virology, Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand; Queen Sirikit National Institute of Child Health, Bangkok, Thailand; Department of Pediatrics, Chulalongkorn Hospital, Bangkok, Thailand; Department of International Health, Center for Immunization Research, Johns Hopkins School of Hygiene and Public Health, Baltimore, MD; U.S. GlaxoSmithKline, Collegeville, PA; Department of Virus Diseases, Division of Communicable Diseases and Immunology, Walter Reed Army Institute of Research, Silver Spring, MD

Dengue virus circulation and association with epidemics and severe dengue disease were studied in hospitalized children with suspected dengue at the Queen Sirikit National Institute of Child Health in Bangkok, Thailand, from 1973 to 1999. Dengue serology was performed on all patients and viral isolation attempted on laboratory-confirmed patients. Acute dengue was diagnosed in 15,569 children and virus isolated from 4,846. DEN-3 was the most frequent serotype in primary dengue (49% of all isolates), DEN-2 in secondary and in dengue hemorrhagic fever (37% and 35%, respectively). The predominant dengue serotype varied by year: DEN-1 from 1990–92, DEN-2 from 1973–86 and 1988–89; DEN-3 in 1987 and 1995–99; and DEN-4 from 1993–94. Only DEN-3 was associated with severe outbreak years. Our findings illustrate the uniqueness of each serotype in producing epidemics and severe disease and underscore the importance of long-term surveillance of dengue serotypes in understanding the epidemiology of these viruses.

INTRODUCTION

Dengue virus (DV) is the causative agent of dengue fever (DF) and dengue hemorrhagic fever (DHF) and consists of four distinct serotypes (DEN-1, DEN-2, DEN-3, and DEN-4).1,2 DHF, the potentially fatal form of dengue virus infection, was first recognized in Bangkok, Thailand, in 1958.3–5 Since then, dengue disease incidence has increased from 9/100,000 in 1958 to 189/100,000 in 1998, with the largest reported incidence of 325/100,000 in 1987.6 Dengue has thus become a severe and intractable public health problem in Thailand.7

Bangkok is the epicenter of dengue in Thailand and the site where the original clinical descriptions of DHF and its association with immunologic priming by a previous dengue infection (secondary dengue infection) were made.3,8–11 The Queen Sirikit National Institute of Child Health (QSNICH), formerly Bangkok Children’s Hospital, has admitted the greatest number of dengue cases for 40 years because it is government-financed, accessible to all, and a widely recognized center of excellence. Since 1973, the QSNICH and the Armed Forces Research Institute of Medical Sciences have collaborated to conduct longitudinal surveillance of dengue in Bangkok. In this report, we present the results of that collaboration to illustrate the long-term circulation and associations with disease severity and large epidemics of the four dengue virus serotypes.

MATERIALS AND METHODS

Study design and sites.

The QSNICH is located in Bangkok, Thailand, and is a Ministry of Public Health tertiary care facility with 538 beds. There is a hemorrhagic fever unit with 15–20 beds and a short-term observation unit with approximately 20 beds.

From 1973, children younger than 18 admitted with suspected dengue had acute and convalescent sera obtained for serology and virus isolation. The attending physician assigned DHF grade at the time of discharge using World Health Organization (WHO) criteria.12 Statistical analysis was performed using SPSS for Windows version 10.0 (SPSS Inc.).

Moderate to severe annual dengue epidemics.

The national annual dengue incidence surveillance was used to classify each year’s epidemic as moderate, or severe6 (Table 1). Dengue incidence per 100,000 was ranked into percentiles; the 50th was 71, the 75th was 134, and 90th was 175. Annual epidemics with an incidence ranging from the 75th to 90th percentile were classified as moderately severe, and those greater than the 90th percentile as severe. Accordingly, there were moderately severe epidemics in 1984, 1985, 1989, 1990, and 1997, and severe epidemics in 1987 and 1998.

Changes in laboratory methodology over time.

Dengue and DHF cases were diagnosed by a number of different virus isolations and/or serologic methods from 1973 to 1999 (Table 2).

Serologic definitions of acute dengue virus infection.

A case without dengue antibody in acute and convalescent sera or stable antibody titers without a 4-fold rise was classified as having no evidence of recent dengue virus infection. Acute primary or secondary dengue virus infection was based on previously published serologic criteria.13 Acute dengue virus infections unclassifiable as primary or secondary were classified as indeterminate.

Statistical analysis.

Statistical analysis was performed using SPSS for Windows version 10.0 (SPSS Inc.). Student’s t test, analysis of variance, and Pearson’s correlation or linear regression are used to determine differences or associations among continuous variables, and χ2 or binomial test for proportions. Backward logistic regression was used to assess the independent influence of a number of factors on dengue disease severity.

RESULTS

From 1973 to 1999, there were 15,376 patients (773 infants and 14,603 older children) with laboratory-confirmed acute dengue virus infection. Infants represent a unique population at risk for severe dengue disease.14,15 Therefore, their demographics and disease outcome are discussed separately, and unless stipulated, subsequent data refer to results from patients 12 months or older.

Specificity of clinical diagnosis.

There was no correlation between year and the number of laboratory-confirmed acute dengue cases of all hospitalized suspected dengue, suggesting that changes over time were not due to changes in hospital admission criteria. There was a correlation between the reported national annual disease incidence and the specificity of diagnosis of children diagnosed as suspected dengue by clinical criteria in our series (r = 0.424, P = 0.028). This suggests that the clinical criteria for acute dengue infection were unchanged and that the likelihood of a child’s having acute dengue depended on the incidence of disease in the population.

Dengue virus isolation rates.

The dengue virus isolation rate was calculated as the number of isolates divided by the number of dengue cases. No more than one dengue serotype was recovered per patient, in contrast to other reports.16 The overall isolation rate in children was 33% and increased during the study period (β = 0.84, P < 0.0001 by linear regression) from 21% in 1973 to a peak of 57% in 1998 (Figure 1).

Annual and seasonal occurrence of dengue and dengue serotypes.

There was a strong correlation between the total number of QSNICH dengue cases and the dengue incidence in the metropolitan Bangkok area (r = 0.90, P < 0.0001, Figure 2) and the nation (r = 0.852, P < 0.0001).6

Dengue in Bangkok peaks during the monsoon months of June to October (Figure 3). Before 1979, few dengue cases occurred during the cool, dry winter months of December and January. Since 1979, dengue cases have occurred year-round. From 1973 to 1986, DEN-2 was the dominant dengue isolate. In 1987, for the first time, DEN-3 became the most frequent isolate. DEN-2 regained predominance in 1988–89, followed by DEN-1 in 1990–92, DEN-4 in 1993–94, and DEN-3 in 1995–9. Each dengue serotype appears to have caused several clearly distinguishable outbreaks at 7- to 9-year intervals.

Patient demographics.

The mean age of patients with dengue was 7.6 years (range 1.1 to 17 years, SD 3.4 years). Mean age for any year varied less than ½ SD from the overall mean, with a small increase in mean age over time (β = 0.49, P = 0.01 by linear regression). The overall modal age was 6 years, which also increased over time from 5 years during 1973–79 to 8 years during 1990–99 (β = 0.50, P = 0.008 by linear regression). There were proportionately more males (52%) than females (48%) (P < 0.001 by binomial test).

Antibody response patterns.

Of all dengue virus infections, 16% were primary dengue infection (Table 3). The proportion with primary dengue increased over time with a 3- to 4-year cyclical oscillation in the rate of primary dengue (Figure 4) (β = 0.67 by linear regression, P < 0.0001). The mean age of children with primary dengue was 6.6 years (SD 3.5) compared with 7.8 years (SD 3.3) for secondary dengue (P < 0. 001, 2-tailed Student’s t test).

Dengue virus serotypes by antibody patterns.

DEN-3 was the most frequent isolate in primary dengue (49%), followed by DEN-1 (44%), DEN-2 (5%), and DEN-4 (2%) (Table 3). There was a correlation between the yearly proportion of primary dengue cases and the isolation of DEN-1 (R = 0.5, P = 0.0007 by Pearson correlation) but no other type, suggesting that Bangkok DEN-1 strains were especially pathogenic among children without immune priming from prior flavivirus infection.

DEN-2 was the most frequent isolate in secondary dengue (37%) followed by DEN-3 (29%), DEN-1 (22%), and DEN-4 (12%). There was a correlation between the yearly proportion of secondary dengue cases and the isolation of DEN-2 (R = 0.5, P = 0.004 by Pearson correlation) but no other type, suggesting that Bangkok DEN-2 strains were more pathogenic among children with immune priming from prior flavivirus infection. Overall, DEN-4 was isolated more often from secondary dengue cases (12%) than primary (2%) (P < 0.0001, χ2). DEN-3 was the most frequent isolate among combined primary and secondary cases, suggesting that Bangkok strains combined pathogenicity attributes of DEN-1 and DEN-2.

Factors associated with severe dengue outbreak years.

DEN-1, DEN-2, or DEN-3 was the dominant isolate during moderately severe dengue outbreak years. In contrast, only DEN-3 was the dominant isolate in the two severe outbreaks. These data further suggest that Bangkok dengue strains have differing ability to elicit severe disease and that DEN-3 has been the most successful.

Dengue antibody pattern and dengue disease severity.

There were 2,396 children (16%) hospitalized with a diagnosis of DF and 11,731 (80%) with DHF (Table 4). Of those with DHF, 16% were diagnosed with DHF grade I, 32% with DHF grade II, 45% with DHF grade III and 7% with DHF grade IV.

DHF was more likely to result from a secondary than a primary infection (odds ratio, 5.0; 95% confidence interval 4.5–5.6). DHF resulting from primary infection was milder: grade I (30% of all primary DHF), grade II (47%), grade III (22%), and grade IV (1.1%) (P < 0.0001 by χ2 for linear trend). Secondary dengue DHF was associated with more-severe DHF: grade I (15% of all secondary DHF), grade II (31%), grade III (47%), and grade IV (7%) (P < 0.0001 by χ2 for linear trend). The proportion of DHF due to primary infection varied yearly from a low of 1% in 1978 to a high of 14% in 1997 and has increased over time (β = 0.61, P = 0.001 by linear regression).

Dengue serotypes and dengue disease severity.

The frequency of isolated dengue serotypes was examined by clinical severity (Table 4). DEN-3 was the most frequent isolate in DF patients (39% of all DF viral isolates) followed by DEN-1 (35%), DEN-2 (17%), and DEN-4 (9%). The frequency of isolated dengue serotypes differed between primary and secondary DF. DEN-3 and DEN-1 were the most frequent isolated dengue serotypes in primary DF (46% each of all primary DF viral isolates) followed by DEN-2 (6%), and DEN-4 (2%). DEN-3 was the most frequent isolated dengue serotype in secondary DF (34% of all secondary DF viral isolates) followed by DEN-1 (29%), DEN-2 (24%), and DEN-4 (13%).

Among DHF cases in children, DEN-2 was the most frequent isolate (35% of all DHF viral isolates) followed by DEN-3 (31%), DEN-1 (24%), and DEN-4 (10%). The frequency of isolated dengue serotypes differed between primary and secondary DHF. DEN-3 was the most frequently isolated dengue serotype in primary DHF (50% of all primary DHF viral isolates) followed by DEN-1 (44%), DEN-2 (4%), and DEN-4 (2%). DEN-2 was the most frequently isolated dengue serotype in secondary DHF (40% of all secondary DHF viral isolates) followed by DEN-3 (28%), DEN-1 (20%), and DEN-4 (12%).

To eliminate the interactions among serologic status, severe dengue years, and dengue serotypes on the presence of DHF, backward logistic regression analysis was used to assess the independent influence of each variable. Secondary dengue (log odds ratio [LOR] 3.8, 95% confidence interval [C.I.] 2.8, 5.1) and dengue serotype (DEN-1 [LOR 1.7, C.I. 1.5, 1.9], DEN-3 [LOR 1.5, C.I. 1.3, 1.7], and DEN-4 [LOR 1.5, C.I. 1.2, 1.9]) each independently contributed to the presence of DHF when the other factors were controlled. Severe dengue year independently contributed to the absence of DHF (LOR 0.8, C.I 0.8, 0.9) and DEN-2 did not independently contribute to DHF (LOR 0.8, 0.7, 1.0).

The overall case-fatality for all years was 0.5%. The peak case-fatality rate was 1.6% during the 1987 severe outbreak. Overall, there was a gradual but not significant decline in case-fatality, with a rate of 0.2% during the last 5 years of the study (β = -0.19, P = 0.33 by linear regression). Case-fatality for primary and secondary dengue did not differ (0.6% and 0.4% respectively, P = 0.27 by χ2) and was similar also among serotypes.

Dengue in infants.

From 1973 to 1999, there were a total of 773 infants with acute dengue virus infection (Table 5). The mean age was 7 months (range 1–12 months, SD 2.4 months) with a modal age of 6 months and an equal representation of males and females (51% and 49%, respectively). The peak number of cases occurred from 6–8 months of age (Figure 5). The total case-fatality among infants with confirmed acute dengue was 11/773 (1.4%) and was greater than the 0.5% case-fatality for all years in children (odds ratio 3.1, 1.5<OR<6.1, P < 0.0001). No trend was noted between year and case-fatality, with only 8 years having deaths from acute dengue.

Dengue virus was isolated in 384 infants (total viral isolation rate of 50%), with DEN-2 the most frequently isolated virus (37% of all isolates) followed by DEN-3 (33%), DEN-1 (26%), and DEN-4 (4%). DEN-1 was the most frequent isolate in DF (41% of DF viral isolates) followed by DEN-2 (28%), DEN-3 (28%), and DEN-4 (3%). DEN-2 was the most frequent isolate in DHF (38% of DHF viral isolates) followed by DEN-3 (32%), DEN-1 (26%) and DEN-4 (4%). Among infants with fatal dengue infection, all four serotypes were isolated: DEN-2 (nine cases), DEN-1 (six), DEN-3 (five), and DEN-4 (three).

DISCUSSION

Based on our results, we have demonstrated the following: All four dengue serotypes circulate continuously in Thailand, with one serotype emerging as the cause of each periodic moderate-to-severe epidemic. Each dengue virus serotype has characteristics that influence the nature of dengue epidemic and disease severity. DEN-1, 2, and 3 are associated with moderately severe dengue epidemic years but only DEN-3 with severe dengue years, suggesting that DEN-3 may possess viral characteristics different from those of the other dengue serotypes that result in large epidemics. DEN-2 and DEN-3 are associated with severe dengue disease, DHF, whereas DEN-4 is found primarily in secondary dengue. DEN-4, unlike the other dengue serotypes, may require pre-existing heterotypic dengue antibody for replication or to produce clinically apparent disease. Severe dengue disease in our series results from a combination of several independent contributing factors including serologic status, severe outbreak years, and the circulating dengue serotype.

Our findings extend the early observations of dengue transmission in Thailand and illustrate the constancy in dengue disease severity and serotypes over time despite an increase in overall disease incidence and virus transmission. In 1962, all four dengue serotypes were isolated in the Bangkok area and associated with the occurrence of severe dengue disease.17–19 Our observations extend these observations by demonstrating the dramatic periodic shifts in the occurrence of the predominant dengue serotype over time.

Multiple factors influence dengue transmission, the cycle of epidemics, and the emergence of new dominant serotypes. Vector density and infection rates reflect access to breeding sources and environmental temperature changes due to urbanization and the El Nino phase of the Southern Oscillation.20–23 Herd susceptibility/immunity and other intrinsic population characteristics are additional factors that presumably influence the emergence of new serotypes and drive high disease rates that create epidemics.24,25

The finding that the yearly proportion of primary dengue cases is correlated to the isolation of DEN-1 and no other dengue serotype suggests that Bangkok DEN-1 strains were more pathogenic among children without immune priming from prior flavivirus infection. The occurrence of more DEN-1 over time may in part explain why the proportion of hospitalized children with primary dengue has increased in our population. Our findings with DEN-1 illustrate the fact that each serotype has unique characteristics manifested in how the disease presents in the population.

Infants represent a unique susceptible population for severe dengue disease. The study of dengue in this group has led to many of our current theories on dengue pathogenesis, maternal antibody, and dengue antibody enhancement.14,15,26,27 Our series demonstrated that case-fatality among infants with confirmed acute dengue was three times greater than that of other children. This may reflect the susceptibility of this population toward complications that arise from plasma leakage and shock syndrome. This may be due to the small amount of volume reserve that exists in infants when plasma leakage occurs, under-recognition of potential DHF in febrile infants, or overtreatment with aggressive volume replacement when volume depletion occurs. The isolation of DEN-2 and DEN-3 as the most frequently isolated virus in infants, as it is for secondary dengue infection in other children, suggests that the characteristics of these viruses in producing severe dengue disease in the host relies more on the presence of heterotypic dengue antibody than immunologic priming of cellular or T-cell immunity.

This frequency of dengue serotype isolation is summarized for all years as DEN-3 > DEN-2 > DEN-1 > DEN-4; for primary dengue, as DEN-3 > DEN-1 > DEN-2 > DEN-4; for secondary dengue, as DEN-2 > DEN-3 > DEN-1 > DEN-4; for all DF patients, as DEN-3 > DEN-1 > DEN-2 > DEN-4; and for all DHF, as DEN-2 > DEN-3 > DEN-1. The high degree of correlation of DEN-1 and DEN-2 isolation rates, and its absence with DEN-3, with primary and secondary dengue suggests a propensity of these serotypes to associate with these serologic responses. Our results also indicate that DEN-4 is unusual in that it is the least frequently isolated serotype in any dengue disease state and is not associated with severe dengue outbreaks, and that 97% of isolates are from secondary dengue infections. These observations underscore the importance of viewing each dengue serotype as a separate virus that has evolved with its own unique viral characteristics and propensity to produce disease in the presence or absence of heterotypic dengue antibody.

Examination of severe dengue disease, DHF, in our series demonstrates that it is primarily a condition of secondary dengue infection, with primary DHF in children associated with milder disease. Dengue serotype isolation and dengue disease severity demonstrate that for children with DF, DEN-3 > DEN-1 > DEN-2 > DEN-4, and for children with DHF, DEN-2 > DEN-3 > DEN-1 > DEN-4.

Over time, there was a subtle change in the demographics of children with hospitalized dengue, with a slight increase in mean age from 7.4–7.8 years and an increase in the modal age from 5 years in 1973 to 8 years in 1999. There also was an increase in the percentage of hospitalized primary dengue over time. These findings suggest that children are getting dengue infection at a later age. These observed changes may be due to the overall improvement in the standard of living in Thailand. Improved housing standards, screens on windows, and reduction of mosquito breeding containers around homes may all contribute to decreasing the intensity of potential exposure to dengue-infected mosquitoes in young children. Dengue infection occurs at an older age, though, as intensity of exposure to dengue-infected mosquitoes increases with greater exposure to the outside environment at home or school. Symptomatic dengue virus infection may be age-dependant and produce more-severe disease in older children and thus might explain the observation that the proportion of hospitalized children with primary dengue is increasing.

Our results suggest that dengue serotypes and their isolation from a spectrum of serologic responses to dengue infection and disease severity is not a random event, and that specific dengue serotypes are more frequently isolated in specific dengue disease states. Our results demonstrate the complexity of the dengue virus transmission and its interaction with the host response, and have important implications in identifying factors to predict severe dengue years, developing interventions to control dengue outbreaks, and developing an effective dengue vaccine.

This longitudinal serotype-specific study of dengue virus over 27 years is unique for its long-term characterization of dengue serology, disease severity, and circulating dengue serotypes and serves as a surveillance model to be instituted by other countries faced with the growing threat of dengue virus infection.

Table 1

Reported total dengue cases and incidence in Thailand, from 1973 to 1999

YearTotal Number of CasesIncidence per 100,000YearTotal Number of CasesIncidence per 100,000
* Moderately severe dengue year. †Severe dengue year. (See Methods for definition.) Source: 6
19738,280211987†174,285325
19748,16020198826,92649
197517,767421989*74,391134
19769,616221990*92,005163
197738,76888199143,51177
197812,54728199241,12571
197911,47825199367,017115
198043,32892199451,68888
198125,67054199560,330102
198222,25046199637,92963
198330,025611997*101,689167
1984*69,1011371998†129,954211
1985*80,076155199924,82640
198627,83753
Table 2

Dengue diagnostic tests at armed forces research institute of medical sciences during study period

MethodologyYears Used During Study Period
*28, †29, ‡30, §31,32, ||33, ¶34, **35,28, ††36, ‡‡13.
Viral isolation and identification
Direct viral plaque on LLC-MK2 cell line.*1973 to 1977.
Mosquito inoculation in Toxorhynchites splendens.1977 to present.
Immunofluorescent antibody identification of serotypes.‡1973 to 1983
Antigen capture enzyme immunoassay for serotype identification.§1981 to present.
Nested serotype-specific polymerase chain reaction.||1995 to present.
Serologic characterization
Hemagglutination inhibition assay.¶1973 to present.
Plaque reduction neutralization test.**1973 to present.
Fluorescent antibody assay.††1973 1987.
IgM/IgG isotype-capture enzyme immunoassay.‡‡1987 to present.
Table 3

Summary of the yearly occurrence of dengue serotypes by primary or secondary dengue infection in children

Viral Isolation by Serotype
Confirmed Dengue by SerologyDEN-1DEN-2DEN-3DEN-4
YearSuspected Dengue CasesIndeterminateTotalInd.TotalInd.TotalInd.TotalInd.Total
*Bold in years indicates moderate to severe dengue hemorrhagic fever years based on national reported rates of dengue. (See Methods.) Bold in serotypes indicates the predominant isolated serotype for that year.
1973131107718821142901121030000
1974142139511093104041531040000
197538523285130900000911031040000
1976171614011470000080810010415
1977486203927419000012843338011214319
197817471156128000012252802020415
197928172273237011214925200000101
19807175954319621201934271379153245110022
1981184101581169430701811902020101
1982185161463165211401121310010303
198338093372348120302712848113011011
198470727590146310000342449819633245451
19855311845244740202042042518023332439
19865772648295170173202401437245360202
198714571061248013541418032584089259601210000
198847741352139445091481506290350000
1989119013493315108247906143513661478193301607
199011431458310976751160191313801411024034012012
199153859287034630360660330334509014014
1992471473350382214406512602758013251053
19937746261416772136158120021142503921280130
19945844740912468523634230234818228257261
199562485419951372423316006123717101014014
199663185412049783103905105120520720404
199716902871170311488441311218711334138118277154101404
199816682131110451368361529197114161489630329428012012
199910791155602169622894115272276309110131028533
Total173771677127192071460336684249125740141852151040611068315951544722484
Table 4

Summary of Dengue Fever and Dengue Hemorrhagic Fever by Year and Dengue Serotype from 1973–1999

Viral Isolation by Serotype
Confirmed dengue by serologyDEN-1DEN-2DEN-3DEN-4
Year and dengue gradeInd.TotalInd.TotalInd.TotalInd.TotalInd.TotalTotal
*Dengue fever
†Dengue hemorrhagic fever
1973
    DF*20021001000010010000
    DHF†77718511132901111020000
    Fatal00000000000000000000
    Unclass.10010000000000000000
1974
    DF1010000000000000000
    DHF6631701102041521030000
    Fatal10011001000000000000
    Unclass.6310371001000010010000
1975
    DF02020000000000000000
    DHF20199122000000911031040000
    Fatal01010000000000000000
    Unclass.3830860000000000000000
1976
    DF00000000000000000000
    DHF411911240000080810010415
    Fatal11020000000000000000
    Unclass.1200210000000000000000
1977
    DF9281380000000000001315
    DHF113646381000012843338011111214
    Fatal00000000000000000000
    Unclass.00000000000000000000
1978
    DF633120000003300000000
    DHF11123116000012222502020415
    Fatal00000000000000000000
    Unclass.00000000000000000000
1979
    DF361100011110200000000
    DHF42192225010104825000000101
    Fatal00000000000000000000
    Unclass.02020000000000000101
1980
    DF2638367730104931600000000
    DHF3350216551131633231266135245110022
    Fatal02020000010100000000
    Unclass.01010000010100000000
1981
    DF0100100101020200000000
    DHF101461157420601611702020101
    Fatal01010000000000000000
    Unclass.01010000000000000000
1982
    DF12211342013010110010101
    DHF41252131010101021200000202
    Fatal00000000000000000000
    Unclass.00000000000000000000
1983
    DF3341381102020202130202
    DHF53011307010102512636090909
    Fatal12030000000010010000
    Unclass.00000000000000000000
1984
    DF7513610000170834181629
    DHF19536105650000235340415524138241
    Fatal13150000001110010101
    Unclass.00000000000000000000
1985
    DF8461550000050513042316
    DHF940424150202037037415019129232
    Fatal12140000000000000011
    Unclass.00000000000000000000
1986
    DF9143515708210111012253100101
    DHF173364357091101291315192260101
    Fatal03030000000000000000
    Unclass.00000000000000000000
1987
    DF44940138750123701010160260000
    DHF5911360119571201927507713800930000
    Fatal3180210101020220020000
    Unclass.00000000000000000000
1988
    DF19540731304090927090000
    DHF21296031732051390404220260000
    Fatal12140000001100000000
    Unclass.00000000000000000000
1989
    DF6510731752419144311014442101304
    DHF68812128922267594212161294151200303
    Fatal13041001010100000000
    Unclass.0110110404030300000000
1990
    DF6813202003531066217019480120404
    DHF76695077139850124112101226160220606
    Fatal03030000000000000101
    Unclass.11021001000000000101
1991
    DF2529054117018010122040202
    DHF31243027418280460310312305011011
    Fatal03030000000000000000
    Unclass.3120151102010100000101
1992
    DF26770103111302404044206119020
    DHF21254027510310411200211607132033
    Fatal01010000010100000000
    Unclass.03030000010100000000
1993
    DF22791102119121050537010018018
    DHF3952705661027037115016111802921100112
    Fatal01010000000000000000
    Unclass.17080000000000000000
1994
    DF1851776424101427620809110
    DHF293475381121224126027216220247150
    Fatal00000000000000000000
    Unclass.0110110000000000000101
1995
    DF4591814455212180912166340101
    DHF3631313502190210480481153165013013
    Fatal00000000000000000000
    Unclass.4150190000040400000000
1996
    DF497901282709050515100250101
    DHF3430703416230290400405390440303
    Fatal00000000000000000000
    Unclass.2260280101060603030000
1997
    DF108188123081724445012012465681100101
    DHF15390412106923944121111231166020552701203
    Fatal04150303011200000000
    Unclass.26746106410418080812162300101
1998
    DF6115418233521228115218273514760202
    DHF149927241100311286165011941236826113342010010
    Fatal02020000000000000000
    Unclass.32733303140707172100000
1999
    DF611041017512182322911215214400538
    DHF52437749610682800611621566283022224
    Fatal00110000000000110000
    Unclass.2193240303020204370101
All Years
    DF696162278239615617720353201451117615820039397681895
    DHF I2721608291909861849279416810182641938265169272
    DHF II434326057375185287133857322143431223502349551466157
    DHF III201504525527130154218676441466542290433621345141
    DHF IV11788180001401421000102241144110011
    DHF Total918107011121173120163924864201234381292230874361140935913381
    Fatal10525672406063940150213
    Unclassified533441240972253403303314327530505
Table 5

Summary of Dengue Fever, Dengue Hemorrhagic Fever, and Dengue Serotypes Among Infants for All Years

% of total viral isolation by serotype
Disease Severity# Viral isolates/total dengueDEN-1DEN-2DEN-3DEN-4
*Dengue fever.
†Dengue hemorrhagic fever.
DF*32/774128283
DHF† I67/1331939366
DHF II168/3632837305
DHF III82/1412639332
DHF IV12/232542330
DHF Total329/6602638324
Fatal9/11067330
Unclassified14/252914507
Total384/7732637334
Figure 1.
Figure 1.

Viral isolation rate of serologically confirmed acute dengue infections during study period.

Citation: The American Journal of Tropical Medicine and Hygiene Am J Trop Med Hyg 68, 2; 10.4269/ajtmh.2003.68.191

Figure 2.
Figure 2.

Armed Forces Research Institued of Medical Sciences serologically confirmed dengue cases and ministry of public health reported incidence for Bangkok, Thailand

Citation: The American Journal of Tropical Medicine and Hygiene Am J Trop Med Hyg 68, 2; 10.4269/ajtmh.2003.68.191

Figure 3.
Figure 3.

Seasonal occurrence of serologically condirmed dengue virus infection and dengue serotypes at the Queen Sirikit National Institute for Child Health from 1973–1999.

Citation: The American Journal of Tropical Medicine and Hygiene Am J Trop Med Hyg 68, 2; 10.4269/ajtmh.2003.68.191

Figure 4.
Figure 4.

Percentage of primary dengue of all diagnosed dengue cases by year

Citation: The American Journal of Tropical Medicine and Hygiene Am J Trop Med Hyg 68, 2; 10.4269/ajtmh.2003.68.191

Figure 5.
Figure 5.

Age distribution of infants with dengue hemorrhagic fever and fatal dengue

Citation: The American Journal of Tropical Medicine and Hygiene Am J Trop Med Hyg 68, 2; 10.4269/ajtmh.2003.68.191

Acknowledgments: We thank the doctors and nurses at the Queen Sirikit National Institute of Child Health for their outstanding patient care and participation in this study, and the staff members at the Department of Virology, Armed Forces Research Institute of Medical Sciences, over the past 27 years who have carefully performed diagnostic testing, data entry, and specimen archival. We also thank Dr. Daniel Libraty for his critical reading of this manuscript and Dr. Scott Halstead for sharing his thoughts and vast knowledge base, and giving his comments and suggestions on improving the manuscript.

Financial support: This work was funded by the U.S. Army Medical Research and Materiel Command, Fort Detrick, MD.

The opinions or assertions contained herein are the private views of the authors and are not to be construed as reflecting the official views of the United States Army or the Department of Defense.

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Author Notes

Reprint requests: Timothy P. Endy, Division of Virology, U.S. Army Medical Research Institute for Infectious Diseases, 1425 Porter St., Fort Detrick, MD 21702-5011
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