Streptococcus pneumoniae carriage and penicillin/ ceftriaxone resistance in hospitalised children in Darwin

Background: The prevalence of resistant Streptococcus pneumoniae (SP) is increasing worldwide. Pneumococcal prevalence and susceptibility patterns are not known for children in the Top End of the Northern Territory.
Aims: To determine the prevalence of nasopharyngeal carriage of pneumococci in children hospitalised in Darwin, and the extent of penicillin and ceftriaxone resistance in these isolates.
Methods: Nasopharyngeal swabs were collected on admission from 85 children who had not received antimicrobials for their admission illness. Antimicrobial resistance was determined following selective culture for SP isolates. Minimal inhibitory concentrations (MICs) for penicillin and ceftriaxone were determined using the E-test method.
Results: The overall prevalence of nasopharyngeal SP carriage was 44%. Carriage occurred more often in Aboriginal children from rural areas (56%) than in urban children (24%) (OR 3.94, 95% CI 1.35 - 11.78, p <0.01). Thirty per cent of isolates were penicillin resistant, 35% were ceftriaxone resistant, and 49% were resistant to at least one of these. One isolate showed high-level resistance to both antimicrobials; all other resistant isolates were of intermediate-level resistance. For the same isolate, MICs for ceftriaxone were more often higher than those for penicillin. Five isolates had intermediate resistance to ceftriaxone whilst remaining sensitive to penicillin.
Conclusions: The prevalence of pneumococcal resistance to penicillin and ceftriaxone in hospitalised children in Darwin is much higher than previously reported in Australia. This has implications for future antimicrobial management and highlights the need for regular regional surveillance of SP resistance. The development of conjugate pneumococcal vaccines for children under two years is a priority.