Hospital-Acquired Pneumonia Caused by Multidrug-Resistant Streptococcus pneumoniae Serotype 15A

Background: Streptococcus pneumoniae remains a common cause of community-acquired pneumonia but is an infrequent pathogen in hospital-acquired pneumonia (HAP). Non-vaccine serotypes of multidrug-resistant (MDR) S. pneumoniae strains have been emerging globally, posing an increased risk of nosocomial infection. Case: A 71-year-old man developed pneumonia on postoperative day 4 following spinal fusion surgery. Despite initial treatment with ampicillin/sulbactam, his condition deteriorated, requiring ICU admission and mechanical ventilation. Microbiological testing confirmed S. pneumoniae as a causative pathogen, and ceftriaxone was empirically administered based on the local antibiogram. However, antimicrobial susceptibility testing revealed resistant profiles to penicillin (minimum inhibitory concentration [MIC], 8 µg/mL), ceftriaxone (MIC, 16 µg/mL), meropenem (MIC, 1 µg/mL), macrolides, and clindamycin, while demonstrating susceptibility to levofloxacin and vancomycin. The therapeutic regimen was subsequently adjusted to levofloxacin, resulting in clinical improvement. The isolate was later identified as serotype 15A, sequence type 63 (ST63). Conclusion: This case highlights that MDR S. pneumoniae can cause early-onset HAP and may not be covered by standard empiric therapies, emphasizing the need for careful evaluation of treatment response. Continued surveillance of infections caused by vaccine-escape clones like MDR serotype 15A is essential, given their increasing clinical relevance.