Heavy rain and floods pave the way for higher HIV prevalence

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Increasing levels of heavy rainfall and flooding may be indicators of a higher burden of HIV, according to research published this September in JAMA Network Open. Cross-sectional research led by Dr Jason Nagata and colleagues at the University of California suggests links between climatic changes (such as heavier rainfall and flooding) and HIV outcomes. 

This was an analysis of nationally representative surveys which collected data from households on a wide range of health issues in 21 countries across sub-Saharan Africa between 2005 and 2017. The team reviewed eligible surveys which included information on HIV testing, geography and how many years people had had heavy rainfall. Heavy rainfall was defined as a deviation from the historical norm of at least 50%. 

The analysis included 283,333 surveys. Around 60% of respondents were women and 40% were men. Their average age was 32 and the age range was 15-59. Around 40% of respondents had finished primary education and 25% hadn’t received any education. The majority (64%) of respondents were married and most participants (67%) lived in rural areas. 


longitudinal study

A study in which information is collected on people over several weeks, months or years. People may be followed forward in time (a prospective study), or information may be collected on past events (a retrospective study).

representative sample

Studies aim to give information that will be applicable to a large group of people (e.g. adults with diagnosed HIV in the UK). Because it is impractical to conduct a study with such a large group, only a sub-group (a sample) takes part in a study. This isn’t a problem as long as the characteristics of the sample are similar to those of the wider group (e.g. in terms of age, gender, CD4 count and years since diagnosis).

key populations

Groups of people who are disproportionately affected by HIV or who are particularly vulnerable to HIV infection. Depending on the context, may include men who have sex with men, transgender people, sex workers, people who inject drugs, adolescent girls, prisoners and migrants.

risky behaviour

In HIV, refers to any behaviour or action that increases an individual’s probability of acquiring or transmitting HIV, such as having unprotected sex, having multiple partners or sharing drug injection equipment.

Overall, 43% of participants had been exposed to at least one year of heavy rainfall in the past 10 years. Seven per cent of respondents were known to be living with HIV and around 5% had been diagnosed with a sexually transmitted infection in the 12-month period before the surveys. During this time, the average number of sexual partners other than a spouse was 0.3.

Following heavy rain, there were small but significant increases in the odds of having HIV (14%), sexually transmitted infections (11%) and the number of sexual partners (12%).

Rural and urban settings

The impact of heavy rainfall was more pronounced for those in rural areas. For example, people living in rural areas experienced an increased likelihood of having HIV of 25%, compared with 2% in urban areas. A possible explanation for this is the heightened impact of depleted agricultural yields and food insecurity in rural areas. Flooding can lead to forced migration and the expansion of sexual networks, creating conditions where people may be exposed to substance use and/or gender-based violence. However, there was no significant difference between rural and urban areas in the number of sexual partners.

The team also considered the possible impact of flooding and rain on accessing clinics and other health services, which would limit access to prevention, testing and treatment.  


The impact of heavy rain was more pronounced in adults aged over 30. They experienced higher rates of acquiring HIV, sexually transmitted infections and were more likely to have more sexual partners in comparison to adults in their 20s and teenagers. For example, adults over 30 had an increased likelihood of having HIV of 17%, compared to 11% for adults in their 20s and no increased likelihood for teenagers.

Whilst these statistics indicate gaps for adults over 30, it is crucial to remember that young people remain a key population. In eastern and southern Africa, 45% of new infections are in people under the age of 25.


Other studies have reported findings that show women are more vulnerable to the poorer health outcomes of climatic events. But the association between heavy rain and prevalence of HIV was only slightly more pronounced in women at 16% vs 12% in men. Women have access to fewer income-earning opportunities than men, so they are more vulnerable to disruptions in income, exacerbating pre-existing inequities.


The study was limited by its use of cross-sectional data, rather than a longitudinal study with incidence data. However, the strength of the data from these large population-based health survey sets makes the case for clear links between heavy rainfall and HIV. As extreme weather events worsen, the relevance of the associations found in this research should inform HIV prevention, services and care.

Whilst still an emerging picture, understanding how climatic changes impact food security, sexual risk behaviour and public health infrastructure is increasingly necessary in education and policy. Climate justice solutions should also account for specific barriers faced by women, people living in rural settings and adults over 30. Results from the study make the case for future research exploring novel pathways that lead to poorer outcomes relating to HIV.


Nagata JM et al. Analysis of Heavy Rainfall in Sub-Saharan Africa and HIV Transmission Risk, HIV Prevalence, and Sexually Transmitted Infections, 2005-2017. JAMA Network Open 5:e2230282, 2022 (open access).