Dynamic of SARS-CoV-2 spread in Bulgaria, 2020-2022

The COVID-19 pandemic is associated with high morbidity and significant mortality worldwide. The objective of this study was to track the circulation pattern of SARS-CoV-2 in Bulgaria over three consecutive years (2020-2022) and to analyze the involvement of SARS-CoV-2 in cases of co-infections. A total of 98 247 clinical samples were tested for SARS-CoV-2 using a Real-Time RT-PCR method and 25.2% of them were positive. The positive rate for SARS-CoV-2 was greater among hospitalized patients compared to outpatients (p<0.05). Approximately 48.3% of all SARS-CoV-2-positive cases were male and 51.7% were female (p<0.05). SARS-CoV-2 positivity was highest in the group of oldest adults (≥65 years) (average 40.6%), and lowest in the group of youngest children (0-5 years) (average 9.4%). Several peaks in the spread of SARS-CoV-2 infections were observed. Among the 1 463 SARS-CoV-2 positive clinical samples examined for the presence of other respiratory viruses, 109 (7.5%) cases of co-infections were found. The greatest variety of co-infections with SARS-CoV-2 and other respiratory viruses was detected during the Omicron wave. Surveillance of SARS-CoV-2 is important to continue in the future in order not to miss the emergence of new genetic variants with increased infectivity, virulence or immune escape.