The impact of environmental factors, mosquito densities, and public health intervention strategies on the incidence rates of dengue virus infection and cases after the large-scale epidemics in Tainan and Kaohsiung Cities, 2008-2011
Date Issued
2012
Date
2012
Author(s)
Tiger Li, Zheng-Rong
Abstract
Southern Taiwan has experienced several epidemics of dengue since 1981. After 1988, the largest-scale dengue virus serotype 1 (DENV-1) epidemic occurred in Tainan City from June 2007 to January 2008, resulted in 1,398 laboratory-confirmed indigenous dengue cases. Kaohsiung City had a two-wave epidemic of dengue/dengue hemorrhagic fever (DHF) from July 2009 to February 2011. The first wave lasted for 29 weeks (July 2009-Feb 2010) with DENV-3 as the major serotype, whereas the second wave lasted for 49 weeks (Mar 2010-Feb 2011) and all the four serotypes of DENV were detected. The objectives of this study were to measure the baseline immunity against DENV in both community and schoolchildren in these two cities, and to provide information for integrated dengue surveillance with mosquito indices, environmental factors and intervention strategies.
Two seroepidemiological studies were conducted in Tainan and Kaohsiung Cities during 2008-2010, involving a community-based study targeting at the Lis (the minimal administrative unit in Taiwan) with high incidence of dengue cases, and a school-based study including schools located in Lis with high or low incidence of dengue cases during the studied epidemics. Anti-dengue NS1 immunoglobulin G (IgG) indirect ELISA, anti-DENV IgM capture ELISA, and neutralization tests were used to screen the serum and determine the infected serotype(s). The epidemiological characteristics and temporal clustering features in the first and second waves of the 2009-2011 epidemic in Kaohsiung City were compared by temporal indices. Hurdle model (truncated negative binomial with log link and binomial with logit link) and stepwise selection by Akaike information criterion (AIC) were used to assess the effect of mosquito indices and environmental factors on the occurrence and incidence of dengue cases.
The anti-dengue NS1 IgG seroprevalence in 4 Lis of Tainan City ranged from 6.1% (3/49) to 28.1% (16/57), and about 70% (17/24) of seropositive subjects were from residents aged beyond 65 years of age. Besides, half of seropositive participants were infected with DENV-1 (12/24), and 41.7% (10/24) had responses against multiple serotypes. Schoolchildren in the 4 schools located in the high incidence areas had relatively low anti-dengue NS1 IgG seroprevalence [0.31% (2/656)-2.34% (3/132)], and 88.9% (8/9) of seropositive schoolchildren were infected with DENV-1. On the other hand, two Lis of Kaohsiung City had 14.0% (12/86) and 21.4% (12/56) participants with past infection(s), and 11.6% (10/86) and 1.8% (1/56) had recent infection during the study period. Schoolchildren also showed low anti-dengue NS1 IgG seroprevalence [0.5% (4/789)-2.1% (4/188)] and DENV seroincidence [0.16% (1/625)-2.6% (5/188)]. Seven schoolchildren in Siaogang and Cianjhen Districts were asymptomatically infected with DENV-4.
The first and second waves of the 2009-2011 epidemic of dengue in Kaohsiung City caused total of 656 and 866 dengue cases and 9 and 7 dengue hemorrhagic fever (DHF) cases, respectively, without differences in age, gender and temporal indices. Lis with DHF cases were significantly associated with high temporal indices during the 2010-2011 epidemic in Kaohsiung City. Hurdle models identified two groups of factors affecting the occurrence and incidence of dengue cases. In the first wave, adult mosquito index (AMI) and rank of container index were positively associated with the occurrence of dengue cases, while density of containers and AMI were positively associated with the incidence of dengue cases. In the second wave, population density and rank of container index had positive effect on the occurrence of dengue cases, whereas density of large breeding sites and density of containers had positive effect on the incidence of dengue cases. For the first district affected by epidemic of dengue, use of aerosol cans in the second wave lasted the epidemic longer than using thermal fog in the first wave (40 versus 25 weeks).
In summary, residents and schoolchildren had low seroprevalence and seroincidence of DENV in Tainan and Kaohsiung Cities, implying that southern Taiwan has not become dengue-endemic. In addition, herd immunity varied against different serotypes of DENV across the studied Lis, reflecting the different proportion of at-risk population for future outbreaks. This serological surveillance detected asymptomatic infection of DENV-4 that most clinical surveillance had missed. Two groups of factors associated with occurrence and/or incidence were valuable for the public health policies. For Lis have not been affected, public health professionals must focus on routine clearance of containers and avoiding people gathering; For Lis have been affected, avoiding mosquito bites and self-management for feverish cases are important. In this study, we proposed the frame of integration of mosquito densities, environmental, intervention strategies and other factors for future works to establish a more effective integrated dengue surveillance system.
Subjects
Dengue
Seroepidemiology
Mosquito density/indices
Environmental factors
Hurdle model
Prevention and control strategies
Public Health Policies
Taiwan
SDGs
Type
thesis
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