Ambient Temperature and Dengue Hospitalisation in Brazil over a 10-year period, 2010-2019: a times series analysis

Background Climate factors are known to influence seasonal patterns of dengue transmission. However, little is known about the effect of extreme heat on the severity of dengue infection, such as hospital admission. We aimed to quantify the effect of ambient temperature on dengue hospitalisation risk in Brazil. Methods We retrieved daily dengue hospitalisation counts by each of 5,570 municipalities across the 27 states of Brazil from 1st of January 2010 to 31st of December 2019, from the Brazilian Public Hospital Admission System (“SIH”). We obtained average daily ambient temperature for each municipality from the ERA5-land product reanalysis. We combined distributed lag non-linear models with time stratified design model framework to pool an estimate for dose-response and lag-response structures for the association of Dengue hospitalisation relative risk (RR) and temperature. We estimated the overall dengue hospitalisation RR for the whole country as well as for each of the five macro-regions by meta-analysing state level estimates. Findings 579,703 hospital admissions due to dengue occurred over the 10 years period of 2010 to 2019. We observed a positive association between high temperatures and high risk of hospitalisation for Brazil and each of the five macro-regions. The overall RR for dengue hospitalisation was at the 50th percentile of temperature distribution 1.40 (95% IC 1.27-1.54) and at 95th percentile of temperature the RR was 1.50 (1.38-1.66) for Brazil, relative to the minimum temperature, which was the one with the lowest risk. We also found lagged effects of heat on hospitalisation, particularly observed on the same day (lag 0) both at the 50th percentile and 95th. Interpretation High temperatures are associated with an increase in the risk of hospitalisation by dengue infection. These findings may guide preparedness and mitigation policies during dengue season outbreaks, particularly on the health-care demand. Funding Conselho Nacional de Pesquisa, Coordenação Nacional de Aperfeiçoamento de Pessoal, Institut de Salud Carlos III. Evidence before this study Temperature can have an effect of aggravating a dengue infection progressing to severe disease requiring hospitalisation. On February 12, 2022, we searched PudMed for the terms “dengue”, “severe or hospital” and “temperature or heat”. Although there is extensive literature on the association of temperature and number of dengue cases, we did not find any study quantifying the association of ambient temperature and hospitalisation by dengue. Quantitative evidence on this association, and how the extreme high temperature augments the risk of hospitalisation by dengue is needed to guide plans of mitigation and preparedness. Added value of this study Our findings show that heat can aggravate an on-going infection of Dengue virus leading to hospitalisation. Average temperatures above 23.96° Celsius degrees, the 50th percentile of temperature distribution over Brazil, represents a risk of over 1.3x to the Minimum Hospitalisation Temperature. An average temperature of 28.68° Celsius degrees, the 95th percentile of temperature distribution, represents a risk of hospitalisation of over 1.4x to the Minimum Hospitalisation Temperature. The South region, which does not have a high incidence of Dengue cases and a colder climate compared to other regions, has a temperature-related risk of hospitalisation of greater magnitude compared to other regions. Implications of all the available evidence Heat exposure plays an important role to the public health policy for mitigating dengue virus burden on the population. Hospitalisation is costly to any health system and can be more impacting on fragile or unprepared health systems as frequently found in countries affected by dengue. Due to its hyperendemicity and its seasonality, dengue can be predicted in mid to long term allowing for better designed early-warnings systems to mitigation measures. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement Conselho Nacional de Pesquisa, Coordenacao Nacional de Aperfeicoamento de Pessoal, Institut de Salud Carlos III. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: All the data were got from the Brazillian Hospital Admission System (SIH), that can be accessed thourgh the link: - http://tabnet.datasus.gov.br/cgi/deftohtm.exe?sih/cnv/qibr.def I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data produced are available online at https://github.com/rafalopespx/dengue\_t2m\_severity_paper [https://github.com/rafalopespx/dengue\_t2m\_severity_paper][1] [1]: https://github.com/rafalopespx/dengue_t2m_severity_paper