Climate variability and water-related infectious diseases in Pacific Island Countries and Territories, a systematic review

Background
Climate induced changes in water-related infectious disease (WRID) transmission are a growing public health concern. The effects of climate on disease vary regionally, as do key socioeconomic modifiers. Regional syntheses are necessary to develop public health tools like risk maps and early warning systems at this scale. There is a high burden of WRID in the Pacific Island Countries and Territories (PICTs). There has been significant work on this topic in the PICTs, however, to date, there has been no regional systematic review of climate variability and WRID.

Methods
We searched the PubMed, Web of Science and Scopus scientific databases in September 2022 using a combination of disease, climate, and country terms. We included studies that evaluated the association between climate or weather variability and a WRID in the PICTs using a quantitative epidemiological design. We assessed risk of bias using validated tools. We analysed spatiotemporal publication patterns, synthesised the outcomes of studies in relation to the international literature and identified missing evidence.

Results & discussion
We identified 45 studies of climate and malaria, dengue, diarrhoea, leptospirosis, and typhoid, which represent major WRIDs of concern in the Pacific Islands. More than half of the studies were set in Papua New Guinea or Fiji. The number of studies published each year increased exponentially over time from the 1980s to present. We found few comparable outcomes per disease and setting across epidemiological studies which limited the potential for meta-analysis. However, we identified consistent increased incidence of diarrhoea, dengue, leptospirosis, and typhoid following extreme weather events, highlighting the necessity for adequate water, sanitation, and hygiene access across the PICTs. Additionally, there were consistent positive associations between temperature and dengue incidence in New Caledonia, highly seasonal malaria in PNG, increased diarrhoea incidence with high and low rainfall, and positive associations between leptospirosis and rainfall. These findings are biologically plausible and consistent with the international literature. Future work on this topic in the PICTs can take advantage of increasingly available health and climate data to consolidate the field across a greater diversity of settings and apply these findings to strengthening climate resilient health systems.