Streptococcus pneumoniae ocular infections, prominent role of unencapsulated isolates in conjunctivitis

The aim of this study was to determine the characteristics and shifts in serotype distribution of pneumococcal isolates causing ocular infections in a region of northern Spain in two periods: 1999–2010 for episodes of conjunctivitis (n = 612) and 1980–2010 for uncommon and more severe non-conjunctival ocular infections (n = 36). All isolates were serotyped and non-typeable isolates were confirmed as unencapsulated by multiplex-PCR of the lytA, ply and cpsA genes. Genotyping was done by pulsed-field gel electrophoresis and multi-locus sequence typing. Most conjunctivitis cases occurred in children under 5 years old (89.5%), and more severe non-conjunctival ocular infections occurred in patients older than 25 years (86.1%). Unencapsulated isolates were detected in 213 conjunctivitis episodes (34.8%) and one non-conjunctival infection (2.8%). Rates of unencapsulated isolates were similar throughout the study. Among 399 conjunctival encapsulated isolates, the most prevalent were serotypes 19A (n = 53), 15B (n = 30), 6A (n = 27), 19F (n = 25), 23F (n = 21) and 6B (n = 17). The most prevalent serotypes in non-conjunctival infections were serotype 3 (n = 4), 23F (n = 4), 6B (n = 3) and 19A (n = 3). Conjunctivitis caused by serotypes included in the hepta-valent pneumococcal conjugate vaccine steadily decreased, accounting for 34.9% (22/63) in 1999–2001, 19.7% (23/117) in 2002–04, 13.6% (33/242) in 2005–07 and 3.2% (6/190) in 2008–10. Among the 213 unencapsulated isolates, 31 different pulsed-field gel electrophoresis patterns were identified. The main clonal complexes (CC) were CC941 (ST941, ST942), CC448 (ST448) and CC344 (ST344, ST3097). CC941 was the predominant CC in 1999–2001, 2002–04 and 2005–07, being replaced by CC448 in 2008–10. The multidrug-resistant CC344 was present throughout the study.