Introduction: Streptococcus pneumoniae is an important human pathogen responsible for both localized infections and invasive pneumococcal disease (IPD). Of particular concern is the increasing resistance to penicillin, the antibiotic of choice for the treatment of pneumococcal infections. As antimicrobial susceptibility varies by geographic location and the site of infection, the treatment guidelines must be derived from the local epidemiology.
Methods: Surveillance was conducted at the Department of Clinical Microbiology, the Clinical Hospital Center Rijeka, in the period of January 2020 to December 2024. Invasive isolates were defined as strains collected from normally sterile sites (blood, pleural fluid, cerebrospinal fluid). The total number of pneumococcal isolates collected from inpatients and outpatients from Primorje-Gorski Kotar County, Croatia, was 925, of which 156 were invasive strains. All strains were tested for their antimicrobial susceptibility, with a focus on penicillin resistance.
Results: The number of invasive isolates was twice as high in the period from 2022 to 2024 than that in the previous two years. More than 50% of invasive strains were isolated from adults over 65 years of age. The resurgence of pneumococcal infections can be explained by the gradual withdrawal of anti-COVID pandemic measures. A large number of all isolates showed a reduced susceptibility to penicillin, with significant differences between invasive and non-invasive strains (28% reduced susceptibility in invasive and 49% in non-invasive strains).
Conclusions: The increasing trend of decreased susceptibility to penicillin observed in non-invasive pneumococcal strains is of great concern, as these strains, which have successfully spread in the population, are an important source of invasive infections and a reservoir of antimicrobial resistance. Rising penicillin resistance rates are affecting the treatment of IPD, especially pneumococcal meningitis. Nevertheless, parenteral penicillin is still the drug of choice for the treatment of pneumococcal pneumonia in Croatia.
