Outbreak of hantavirus disease caused by Puumala virus, Croatia, 2021

In 2021, a large outbreak of hantavirus disease (HAVID) in Croatia with 334 notified cases coincided with a COVID-19 wave and included patients from areas previously not considered endemic, challenging HAVID recognition and patient management. We analysed clinical and epidemiological data on all 254 patients with HAVID treated in the Clinical Hospital Center Rijeka (CHC Rijeka) between February and November 2021. Most patients (n = 246; 96.9%) had antibodies against Puumala virus, 212 (83.5%) were residents of endemic areas for HAVID, 93 (36.6%) reported occupational exposure and 86 (33.9%) had observed rodents or rodent excreta. Thirty-seven (14.6%) patients were not notified to the public health authorities. Most patients (n = 177; 69.7%) were male. The median age of the patients was 43 years (range: 17-79 years) in males and 54 years (range: 14-77 years) in females. More severe courses of disease were observed in males aged < 45 years than in older males and females of any age (OR = 2.27; 95% CI: 1.21-4.24; p < 0.005). Measures to prevent exposure, early detection and notification of cases and close collaboration between primary and secondary healthcare teams with public health personnel are essential to improve surveillance and prevent hantavirus outbreaks.