Streptococcus pneumoniae colonisation in a cohort of SE Asian infants

Turner, Paul (2012). Streptococcus pneumoniae colonisation in a cohort of SE Asian infants. PhD thesis The Open University.



Background:Streptococcus pneumoniae is a leading cause of childhood mortality and morbidity. Nasopharyngeal colonisation precedes infection but the dynamics, modifiers, and immunological outcomes of colonisation in infancy are incompletely understood.

Methods: We conducted a longitudinal pneumococcal colonisation study of mothers and infants in Maela refugee camp in NW Thailand. 965 infants were followed from birth until 24 months.

Results: Pneumococcal colonisation occurred early in infancy (median 46d). Vaccine serotypes (PCVI3) accounted for 55.8% of isolates from infants and 27.5% from mothers. II Non-typeable pneumococcal colonisation was commOD. Previous colonisation did not result in protection against subsequent pneumococcal acquisitions in infancy, although serotype reacquisitions tended. to be delayed and of shorter duration.

Positive associations were found between colonisation by pneumococci and Haemophilus influenzae (OR 2.9, P<.001) or Moraxella catarrhalis (OR 2.1, P<.001), whereas Staphylococcus aureus colonisation was negatively 3associated (OR 0.3, P<.001 ). During first pneumonia episodes, detection of respiratory syncytial virus was negatively associated with pneumococcal colonisation (OR 0.5, P=.02).

Serum IgG anti-capsular antibody responses to colonisation varied by capsule and increased with age: these antibodies were not protective against colonisation in infancy_ Although cord bloods had high titres of IgG to pneumococcal surface and virulence , proteins, none were associated with delayed infant colonisation. These proteins were immunogenic in infants but antibodies did not protect against colonisation. Latex sweep serotyping was 3.9 times, and microarray 4.4 times, more likely to detect multiple pneumococcal serotype co-colomsations than standard WHO protocol culture (P<.001).

Conclusions: Pneumococcal colonisation is influenced by previous exposure to homologous and heterologous serotypes. Neither previous exposure nor serum antibodies to capsule or surface proteins protect against colonisation in the first 24 months of life. WHO methodology significantly underestimates multiple serotype colonisations. These colonisation data will be a valuable baseline to compare with future studies following regional introduction of pneumococcal conjugate vaccines.

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