Baseline epidemiology study of nasopharyngeal carriage and serotypes of Streptococcus pneumoniae in children aged 6-59 months prior to the introduction of pneumococcal conjugate vaccine in Iran

BACKGROUND AND AIM: This study aimed to assess the prevalence, serotype distribution, and antimicrobial susceptibility of Streptococcus pneumoniae (S. pneumoniae) in children aged 6-59 months in Iran, prior to introducing pneumococcal conjugate vaccine (PCV). METHODS: Nasopharyngeal (NP) samples were collected from unvaccinated children aged 6-59 months in this multicenter study. S. pneumoniae was identified using culture methods along with biochemical characteristics and confirmed by real-time PCR. Antibiotic resistance testing was performed utilizing the MIC method. Serotyping was accomplished through the utilization of the Quellung test. RESULTS: Of the 1063 nasopharynx isolates, 20.4% carried pneumococcus in NP. The five most common isolated serotypes were 23 F, 19 F, 14, 15B and 6 A. High frequency of 15B, as non-vaccine serotypes (NVTs), was observed. Approximately 20% of the isolates were non-susceptible to penicillin, while low resistance rates were recorded against ceftriaxone (8.7%). Overall, 25.4% of pneumococcal strains exhibited multidrug resistance (MDR). The serotype coverage of PCV7, PCV10, and PCV13 were determined as 42.5%, 54.7%, and 61.8%, respectively. CONCLUSIONS: S. pneumoniae was detected in 20.4% Iranian children's NP samples, with the serotype 23 F dominancy. Emerging of 15B and lower PCVs prediction coverage compared to other unvaccinated countries, might stem from limited administration of PCV13, environmental/epidemiological factors, and COVID-19-related shifts in colonization. Ongoing surveillance of pneumococcal carriage, serotype distribution, and antimicrobial resistance are required due to the existence of antibiotic resistance and MDR isolates.