Association of climate variability with hepatitis A and E infections in Dhaka (2016–2023)

Acute viral hepatitis (AVH) is a pressing global public health issue due to its significant contribution to morbidity and mortality worldwide [1]. This is more apparent in low- and middle-income countries where the availability of proper sanitation infrastructure, access to clean water and safe hygiene practices are lacking [2]. Several hepatotropic viruses—including Hepatitis A, B, C, D, and E—can cause acute viral hepatitis (AVH), but hepatitis A virus (HAV) and hepatitis E virus (HEV) are the most common enterically transmitted types. Both are primarily spread via the faecal-oral route, typically through contaminated food or water. Clinical symptoms include fever, nausea, vomiting, loss of appetite, abdominal pain, and jaundice, with severity ranging from asymptomatic to fulminant hepatic failure. An estimated 1.4 million new cases of HAV and approximately 20 million new cases of HEV are reported globally each year [3]. Addressing this morbidity and mortality burden remains a major public health challenge, especially in resource-constrained endemic settings.

Bangladesh, endemic for viral hepatitis and the transmission of HAV and HEV is influenced by socio-demographic and environmental conditions [4, 5]. The environment supports the persistence and transmission of enteric viruses due to poor sanitation, limited access to clean water, unhygienic practices, and widespread consumption of unsafe street food [6]. Moreover, distinct climatic variability due to the nature of Bangladesh’s tropical climate–characterised by high humidity, heavy precipitation and temperature variation – is linked to changes in transmission dynamics [7, 8, 9]. Unplanned urbanisation, overcrowding further contribute to the sustained transmission of HAV and HEV [10].

A nationwide surveillance reporting hepatitis A in approximately 19% of cases and hepatitis E in about 10% [11] and several existing research on acute HAV and HEV-related viral hepatitis from the country has primarily focused on clinical and demographic risk factors, often overlooking the precise influence that meteorological variables, particularly within the local context [12]. This knowledge gap is especially critical given Bangladesh’s climate vulnerability from the effects of climate change in the coming years [13]. Despite the established endemicity of HAV and HEV, there remains a gap in understanding how their prevalence correlates with demographic and climatic variability in Dhaka city. The city’s dense population and rapid urbanisation have created major public health challenges, including poor sanitation, unsafe street food practices, inadequate drainage, and air pollution—conditions that facilitate frequent disease outbreaks [10]. Addressing such issues are paramount for developing effective disease forecasting, outbreak preparedness and evidence-based public health interventions within the epidemiological landscape of the city. Therefore, this study aimed to explore the seroprevalence of acute HAV and HEV infections in Dhaka city, with the intention of gaining a better understanding of how weather conditions influence the transmission of hepatitis A and E in a crowded city with numerous health risks.

Between 2016 and 2023, a total of 19,542 and 23,249 suspected AVH patients were tested for anti-HAV-IgM and anti-HEV-IgM, respectively. Among these, 5,767 (29.6%) tested positive for anti-HAV-IgM, and 4,780 (20.5%) for anti-HEV-IgM. A breakdown by gender showed that males accounted for the majority of positive cases in both infections. The prevalence of dual HAV and HEV infection was 85 (0.6%), with a male predominance of 72.9%. Age categorisation by each decade of life showed that anti-HAV-IgM was most frequently detected among younger individuals. In contrast, anti-HEV-IgM was predominantly observed among young adults, with the highest proportion (40.6%) occurring in the 21–30 age group. For dual infections, those aged 11 to 30 years were the most affected group (Table 1).

This study investigates the month-wise (Figure 1) and season-wise (Figure 2) infection patterns of HAV and HEV in relation to meteorological variables—temperature (°C), humidity (%), and rainfall (mm). Monthly analysis reveals that fluctuations in humidity coincide with both HAV and HEV (Supplementary Figure 1) cases, with HEV showing a stronger association. Both infections exhibit a proportional rise and fall throughout the year, with rainfall emerging as a key environmental driver. In July, the peak month, HAV and HEV cases reached 10% and 11%, respectively, alongside a rainfall level of 345 mm. HAV transmission was most prominent during the warmer months with moderate rainfall, particularly from July to November, while HEV transmission peaked during months characterised by high humidity and precipitation, spanning March through September. Seasonal climatic analysis further affirmed these trends (Supplementary Figure 2). HAV infections were most prevalent in autumn (19%) and late autumn (20%), despite declining temperature (27.8°C), humidity (69.8%), and rainfall (62.3 mm). In contrast, HEV infections peaked during the summer (18%) and rainy season (19%), aligning with elevated humidity levels (75.6–78.7%) and high rainfall (287–289 mm).

A multivariable logistic regression model using continuous predictors identified several significant associations (Table 2). Demographic and temporal factors were identified as significant predictors of infection. Compared to males, females had slightly higher odds of HAV infection (OR 1.1; 95% CI 1.1–1.2) but were significantly less likely to test positive for HEV (OR 0.8; 95% CI 0.8–0.9). When age groups were compared against the reference category of ≤10 years, the odds of HAV infection declined with increasing age. However, HEV showed the opposite trend, with the 21–30 age group demonstrating the highest risk (OR 2.5; 95% CI 2.0–3.1). Temporal trends were also evident. Compared to January, the odds of HEV infection increased sharply between April and September, with the highest risks recorded in June (OR 15.5; 95% CI 11.6–20.7). HAV did not exhibit such pronounced monthly fluctuations, although the odds were lowest from February to May (P<0.05) compared to other months. In terms of seasons, Late Autumn was associated with significantly lower odds of HEV infection (OR 0.8; 95% CI 0.7–0.9), while no seasonal variation reached statistical significance for HAV.