The burden of dengue and force of infection among children in Kerala, India; seroprevalence estimates from Government of Kerala-WHO Dengue study

Background

Dengue shows high geographic heterogeneity within and across endemic countries. In the context of increasing burden and predicted outbreaks due to climate change, understanding the heterogeneity will enable us to develop region specific targeted interventions, including vaccination. World Health Organisation (WHO) suggests standard methodologies to study the burden and heterogeneity at national and subnational levels. Regional studies with robust and standard methodology to capture heterogeneity are scarce. We estimated the seroprevalence of dengue in children aged 9-12 years and the force of infection in Kerala, India, from where Zika cases also have been reported recently.

Methods

We conducted a school-based cross-sectional survey in 38 clusters; selected by stratified random sampling, representing rural, urban, high burden and low-burden administrative units. Validation of Indirect IgG ELISA was done by Plaque Reduction Neutralization Test (PRNT90) using the local isolates of all four serotypes. Force of infection (FOI) was estimated using the WHO-FOI calculator. We conducted a follow-up survey among a subsample of seronegative children, to estimate the rate of sero-conversion.

Results

Among 5236 children tested, 1521 were positive for anti-dengue IgG antibody. The overall seroprevalence in the state was 29% (95% CI 24.1-33.9). The validity corrected seroprevalence was 30.9% in the overall sample, 46.9% in Thiruvananthapuram, 26.9% in Kozhikkode and 24.9% in Kollam. Age-specific seroprevalence increased with age; 25.7% at 9 years, 29.5% at 10 years, 30.9% at 11 years and 33.9% at 12 years. Seroprevalence varied widely across clusters (16.1%-71.4%). The estimated force of infection was 3.3/100 person-years and the seroconversion rate was 4.8/100 person-years. 90% of children who tested positive were not aware of dengue infection. All the four serotypes were identified in PRNT and 40% of positive samples had antibodies against multiple serotypes.

Interpretation

The study validates the WHO methodology for dengue serosurveys and confirms its feasibility in a community setting. The overall seroprevalence in the 9-12 year age group is low to moderate in Kerala; there are regional variations; high burden and low burden clusters co-exist in the same districts. The actual burden of dengue exceeds the reported numbers. Heterogeneity in prevalence, the high proportion of inapparent dengue and the hyperendemic situation suggest the need for region-specific and targeted interventions, including vaccination.

Funding

World Health Organization.

A predictive score for severity in patients with confirmed dengue fever in a tertiary care hospital in Kerala, India

BACKGROUND

The study aimed to identify predictors of severe dengue during the 2017 epidemic and to develop and validate a simple predictive score for severity.

METHODS

A retrospective analytical study was conducted using clinical and laboratory data from adult dengue patients with a confirmed microbiological diagnosis. The study included patients who presented to a tertiary care centre in Kerala, India, during the febrile phase (≤4 d) between June 2017 and February 2019. Using appropriate statistical tests, we derived predictors of severe disease and computed a risk score model.

RESULTS

Of the 153 patients (mean age 50±17 y; 64% males), 31 (20%) had severe dengue and 4 (3%) died. Petechial lesions, hypoalbuminemia (<3.5 g/dl), elevated alanine aminotransferase (>40 IU/l) and urea >40 IU/l were significant predictors. Our scoring system (cut-off: 2) showed excellent performance, with an area under the receiver operating characteristics curve of 0.9741, sensitivity of 100%, specificity of 96% and accuracy of 98%. The risk score was secondarily validated on 48 patients hospitalized from March 2019 to June 2019.

CONCLUSION

Our scoring system is easy to implement and will help primary healthcare practitioners in promptly identifying severe dengue cases upon hospital presentation.

Region-specific improvisation on WHO case definition and environmental risk factors associated with dengue: a case-control analysis from Kerala, India

BACKGROUND

Region-specific variations may occur in symptomatic manifestations that need to be addressed by dynamic case definitions. Environmental risk factors for dengue also vary widely across geographic settings. Our aim was to study the test positivity rate of the World Health Organization (WHO) 2009 probable dengue case definition and to suggest region-specific improvisations to it. The study also analyses the sociodemographic and environmental risk factors of dengue fever in South Kerala, India.

METHODS

A case-control study was conducted in South Kerala from 2017 to 2019. Dengue reverse transcription polymerase chain reaction (RT-PCR)-positive and RT-PCR-negative 'probable dengue' patients were compared to identify significant symptoms for a modified definition of dengue. A group of afebrile community controls was compared with RT-PCR-positive dengue cases to study the environmental and behavioural risk factors.

RESULTS

Arthralgia, palmar erythema and rashes have high discriminatory power (odds ratio [OR] >3) for identifying dengue. Redness of eyes, altered consciousness, abdominal distension and chills were found to moderately discriminate (OR 2-3) dengue. The adjusted analysis showed the presence of mosquito breeding sites (indoor p=0.02, outdoor p=0.03), solid waste dumping (p<0.001) and open water drainage in the compound (p=0.007) as significant predictors.

CONCLUSIONS

Regional modifications should be considered when using the WHO definition in endemic settings. Control of mosquito breeding at the household level is the key towards dengue prevention.

Genetic characterization of dengue virus from patients presenting multi-serotypic infections in the Northern West Bengal, India

Northern West Bengal, popularly known as North Bengal, is a dengue-endemic area, which has been severely affected by Dengue in the past few years resulting in massive hospitalizations and deaths. Genetic characterization of the circulating endemic dengue virus (DENV) serotypes is of paramount importance for the epidemiological understanding of the infection and subsequent vaccine development. The present study was conceived to characterize circulating dengue serotypes and to undertake phylogenetic study. EDTA blood samples of all (N = 83) NS1-positive cases of patients with acute febrile illness referred to different health care facilities were collected and processed for RNA isolation followed by the complementary DNA (cDNA) preparation. Serotype determination of dengue infection was done using conventional PCR by targeting the viral C-prM region. Phylogenetic tree was constructed by implementing the Maximum likelihood method. Out of 83 blood samples 17 were detected to be positive for the presence of dengue viral RNA. DENV3 was found to be the predominant serotype in the single-infection cases; however, we have detected multi-serotypic co-infections throughout the study. Joint pain was found to be the most valuable symptom for the prognosis of dengue. Sequence analyses suggested that both DENV1- and DENV3-circulating genotypes are in the genotype III group and remain closely related to the Indian clade. To the best of our knowledge, this is the first report on the genetic characterization of circulating DENVs in North Bengal, which may contribute to the study of dengue epidemic and pathogenesis.