Outbreak of Hepatitis A: Associated Risk Factors and Control Measures

Hepatitis A (HA) is an infection caused by the hepatitis A virus (HAV). Transmission occurs predominantly through the fecal-oral route by ingestion of contaminated water or food and/or intimate contact with an infected individual. The infectious period usually begins one to two weeks before symptom onset, when cases are still asymptomatic, increasing transmission and complicating HA control. It is commonly considered a sexually transmitted infection, particularly among men who have sex with men (MSM). During sexual intercourse, contamination may occur through oral-anal, digital-anal, and genital-oral contact with an infected partner. In September 2024, after identifying an increase in hospitalized HA cases from the private sector that had not been reported, the municipality intensified surveillance, characterizing an outbreak starting in December 2023 and initiating an investigation to define the epidemiological profile of cases and identify risk factors associated with increased HA detection. Identification of additional unreported cases through systematic review of reactive anti-HAV IgM tests from private laboratories and the municipal laboratory. A case-control study was conducted, complemented by descriptive analysis of hospitalized cases, in partnership with CIEVS-MG and the Ministry of Health. Between December 2023 and May 2025, 355 HA cases were identified, 75% of them male, 83% aged 20–44 years, 10.5% HIV-positive, and 12.1% users of pre-exposure prophylaxis (PrEP). In the case-control study, bivariate analysis indicated the following risk factors for HA: MSM, oral-anal sex, anal sex, water treated by household filters, consumption of food from street vendors, and consumption of frozen fruits. In multivariate analysis using hierarchical logistic regression, oral-anal sex remained independently associated with hepatitis A (Crude OR 4.29; 95% CI [1.16–15.84]; P = 0.034) (Adjusted OR 5.45; 95% CI [1.39–21.28]; P = 0.015). The findings demonstrate the sexual nature of the HA outbreak in the municipality. Among the implemented control measures, hepatitis A vaccination was expanded starting April 16th, 2025, to PrEP users, sexual and household contacts aged 11–44 years of confirmed HA cases.