Does Climate Matter to Human Rabies Lethality? An Ecological Study in Vietnam, 1997-2015

Abstract

Background: Rabies remains as one of the neglected zoonotic diseases. Although its incidence shows seasonal pattern, how the climate conditions affect mortality of rabies is rarely known. Methods: An ecological study was conducted in two provinces of seven ecological regions in Vietnam, using Human Rabies Surveillance Data of Vietnam between 1997 and 2015. Monthly rabies post-exposure prophylaxis (PEP) cases, monthly human death cases from rabies, and climate characteristics were collected. Using Poisson regression, we estimated the association between monthly human rabies death cases and air temperature, humidity, precipitation, and sunshine duration in both PEP-used and PEP-not-used group. Findings: 2390 place (province)-time (specific year-month) ecological measurements with 920 510 PEP cases were included in this study. Twenty-two death cases were recorded in PEP-used group, while 344 patients without PEP were died from rabies. There was significant positive association between absolute humidity and death cases in PEP-used group (coefficient 0·3367 [95% CI: 0·0618 to 0·6115]). Human rabies deaths in PEP-not-used group are increased by higher absolute humidity, and lower monthly average air temperature, monthly total precipitation and sunshine duration. Interpretation: Lowering absolute humidity might be helpful for the suspicious rabid animal bite victim to prevent rabies death. Inverse relationship between average temperature and human rabies death in PEP-not-used group suggests ambient temperature modulation of the Milwaukee Protocol should be reassessed. Our findings can be applied to patients who are exposed to rabid animals along with further experimental researches for better treatment. Funding Statement: Seoul National University College of Medicine; Ministry of Health, Vietnam. Declaration of Interests: The authors declare no competing interests. Ethics Approval Statement: For the data collection, the certificate of approval from the institutional review board at NIHE was obtained (IRB-VN01057-07/2017). Since this study protocol did not use the information of individual patients directly, no additional ethical approval was required.