Abstract
Background:
Invasive pneumococcal infections (IPIs), such as bacteremia, pneumonia, and meningitis, pose a significant risk to children <2 years and adults >65 years. The prevalence of serotypes causing IPIs varies over time and geographically. The increased use of pneumococcal polysaccharide (PPV)-23 for >65 years and pneumococcal conjugate vaccine (PCV)-13 for <2 years has led to the rise in non-vaccine serotypes in the world. The choice of antibiotics to treat IPIs has become a real challenge due to antimicrobial resistance.

Aim:
This study aimed to check the coverage of the vaccines and the effectiveness of locally recommended antibiotics for IPIs.

Methods:
This retrospective study was performed in East Sussex Healthcare Trust from January 2006 to December 2018.

Results:
A total of 523 invasive pneumococcal isolates were recovered from sterile samples from 491 patients. Of these, 498 were from blood cultures, and 16, 5, and 4 each were from cerebrospinal fluid (CSF), joint fluid, and pleural fluid, respectively. More than one specimen yielded Streptococcus Pneumoniae (S. pneumoniae): 12 of 491 patients had both CSF and blood culture, 2 had blood culture and joint fluid, and 1 had blood culture and pleural fluid. All 523 isolates were subjected to Quellung serotyping and antimicrobial susceptibility testing. Forty-nine different serotypes were observed; 68% (357/523) of these serotypes come under pneumococcal vaccine coverage. The prevalent serotypes were 12F (9%), 8 (9%), 19A (7%), 3 (6%), 7F (5%), 9N (5%), and 22F (4%), while 32 isolates were undetermined. Serotype 23B was isolated from 5 patients. The vaccine serotype coverage of PCV13 and PPV23 against serotypes causing IPIs was 34% and 68%, respectively. Among patients aged <2 years, 35% of isolates belonged to serotypes covered by PCV13, while among patients aged >2 years, 68% of isolates belonged to serotypes covered by PPV23. Antimicrobial susceptibility results showed that more than 93% of S. pneumoniae were sensitive to penicillin, amoxicillin, and cefuroxime, while <1% were resistant to penicillin.

Conclusion:
Locally recommended antibiotics are effective against IPIs. Inclusion of 15A and 23B in the vaccine would improve the PCV-13 and PPV-23 performance in IPI prevention. Continuous surveillance of serotype distribution and antimicrobial susceptibility is important for appropriate use of antimicrobials to avoid antimicrobial resistance, plus serves as important data for vaccinologists.

Key words: Invasive pneumococcal infection; Pneumococcal vaccine; Serotype.