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During the four pandemic waves, a total of 560,504 cases and 10,178 deaths due to COVID-19 were reported in Croatia. The Alpha variant, dominant from March 2021 (>50% of positive samples), was rapidly replaced by Delta variants (>90%) by August 2021. Several seroprevalence studies were conducted in different populations (general population, children/adolescents, professional athletes, healthcare workers, veterinarians) and in immunocompromised patients (hemodialysis patients, liver/kidney transplant recipients). After the first pandemic wave, seroprevalence rates of neutralizing (NT) antibodies were reported to be 0.2–5.5%. Significantly higher seropositivity was detected during/after the second wave, 2.6–18.7%. Two studies conducted in pet animals (February-June 2020/July–December 2020) reported SARS-CoV-2 NT antibodies in 0.76% of cats and 0.31–14.69% of dogs, respectively. SARS-CoV-2 NT antibodies were not detected in wildlife. Environmental samples taken in the households of COVID-19 patients showed high-touch personal objects as most frequently contaminated (17.3%), followed by surfaces in patients’ rooms (14.6%), kitchens (13.3%) and bathrooms (8.3%). SARS-CoV-2 RNA was also detected in 96.8% affluent water samples, while all effluent water samples tested negative. Detection of SARS-CoV-2 in humans, animals and the environment suggests that the ‘One Health’ approach is critical to controlling COVID-19 and future pandemics.

Over a year into the COVID-19 pandemic, there is growing evidence that SARS-CoV-2 infections among dogs are more common than previously thought. In this study, the prevalence of SARS-CoV-2 antibodies was investigated in two dog populations. The first group was comprised of 1069 dogs admitted to the Veterinary Teaching Hospital for any given reason. The second group included dogs that shared households with confirmed COVID-19 cases in humans. This study group numbered 78 dogs. In COVID-19 infected households, 43.9% tested ELISA positive, and neutralising antibodies were detected in 25.64% of dogs. Those data are comparable with the secondary attack rate in the human population. With 14.69% of dogs in the general population testing ELISA positive, there was a surge of SARS-CoV-2 infections within the dog population amid the second wave of the pandemic. Noticeably seroprevalence of SARS-CoV-2 in the dog and the human population did not differ at the end of the study period. Male sex, breed and age were identified as significant risk factors. This study gives strong evidence that while acute dog infections are mostly asymptomatic, they can pose a significant risk to dog health. Due to the retrospective nature of this study, samples for viral isolation and PCR were unavailable. Still, seropositive dogs had a 1.97 times greater risk for developing central nervous symptoms.

The Croatian Institute of Public Health (CIPH), as the institution responsible for national health statistics, was in early March 2020 confronted with a serious challenge. After the official declaration of the coronavirus disease 2019 (COVID19) epidemic, CIPH had to provide adequate resources for the surveillance of a wide array of epidemiological parameters on a short notice, which was necessary to manage the current public health crisis. It is noteworthy that at the time, Croatia, like many other countries in the European Union and worldwide, did not have a surveillance system established for this particular purpose. Fortunately, the Croatian health authorities managed to mobilize a broad inter-sector cooperation under CIPH coordination and established a functional surveillance system;this system now provides information to the National Civil Protection Directorate (NCPD), county Civil Protection Directorates, European institutions (such as the European Centre for Disease Prevention and Control), expert workgroups, national media, etc. In collaboration with the Ministry of Science and Education, CIPH also monitors the data on the number of SARSCoV-2-infected and self-isolated students and teachers. These data are obtained by matching personal identification numbers contained in the central test result database with those in the electronic register containing information on all students and teachers in elementary and high schools. The establishment of this surveillance system provided the basis for a timely and adequate epidemic response. The longer-term evaluation also allows for monitoring of various trends and projections development, which are useful for concurrent decision-making and preparations toward anticipated events.