Carriage and distribution of serotypes Streptococcus pneumoniae in healthy vaccinated children for the year 2021 in Bulgaria

Streptococcus pneumoniae is one of the common causes of disease in children like pneumonia, otitis and meningitis. Pneumococci colonize asymptomatically the nasopharynx and could cause severe life-threatening illnesses. Since 2010, the 10-valent pneumococcal conjugate vaccine (PCV-10) has been included in Bulgaria for routine immunization of children from 6 weeks to 2 years. For the period 2011-2019 the coverage with it is considered to be 90%.
The aim of the present study is to determine the frequency of carriers and common serotypes of S. pneumoniae from nasopharyngeal isolates of children in 2021, more than ten years after the introduction of PCV10 in Bulgaria.
Nasopharyngeal swabs were taken from 220 vaccinated children, aged 5 months to 5 years old, collected from January 2021 to December 2021. Molecular detection methods were used – polymerase chain reaction (PCR) for detection and typing. By amplification of the lytA gene S. pneumoniae was detected in the taken nasopharyngeal isolates, and by amplification of the cpsA gene capsule abundance was determined. Typing was performed by PCR and allelic hybridization.
The results show a total of 73 positive for Streptococcus pneumoniae samples (33.2%). The most common serogroup/serotypes determined in carriers was 19B/19C (15%) followed by serotypes/serogroups – 15B/15C (8%), 23B (8%) and 10F/10C (7, 1%). In conclusion from the presented data, we estimate a high percentage of carriers in Bulgarian children, characterized mainly by non-vaccine serotypes in the pneumococcal populations.