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Pneumococcal invasive isolates of non-vaccine serotypes in Italy, 1999–2003 (pre-vaccine era)

Abstract number: 1733_494

Gherardi G., Monaco M., Camilli R., D'Ambrosio F., D'Ancona P., Manganelli R., Dicuonzo G., Pantosti A.

Objectives: The introduction of the 7-valent conjugate vaccine (PCV7) for children has caused a dramatic decrease of pneumococcal infections due to vaccine serotypes (VS) and a relative increase of infections due to vaccine-related (VRS) or non-vaccine serotypes (NVS). The aim of this study was to characterise invasive pneumococci belonging to serotypes non included in PCV7 before the implementation of this vaccine in Italy.

Methods: All pneumococcal invasive isolates recovered from children and adults in an Italian nation-wide surveillance in 1999–2003 were studied. All isolates were serotyped and examined for susceptibility to penicillin, cefotaxime, erythromycin, clindamycin, tetracycline and chloramphenicol following the CLSI standard procedures. Pulsed-Field Gel Electrophoresis and Multilocus Sequence Typing (MLST) were used to define clonal groups among penicillin non-susceptible (PNSSP) and/or multi-drug resistant isolates and selected susceptible isolates. The sequence types (ST) were related to those reported in the MLST website (www.mlst.net) and described in the Pneumococcal Molecular Epidemiology Network (PMEN) as international clones.

Results: Among 790 invasive isolates, mostly obtained from adult patients, 392 (49.6%) belonged to VS; the other group included isolates belonging to VRS (93 isolates), to NVS (297 isolates) or that were non-typable (8 isolates). Among these isolates, 19 (5.7%) were PNSSP, all in the intermediate range, and 63 (15.8%) were erythromycin-resistant. The most prevalent serotypes, were 6A, and 19A among VRS and 1, 3, 7F, 8, 10A, 11A, 12F, 15B/C, 20 and 22F among NVS. Among the PNSSP the most frequent serotypes were 19A and 35F (5 isolates each). Several PMEN clones were identified, such as Sweden15A-25/ST63, Greece21–30/ST193, Netherlands3–31/ST180, Netherlands8–33/ST53, Netherlands15B-37/ST199, Netherlands7F-39/ST191 and Sweden1–40/ST304. Some cases of capsular switching were detected. Some isolates belonged to clonal groups that had not been previously identified, such as serotype 15B/C isolates (ST1577) and serotype 6A isolates (ST675 and ST1833).

Conclusions: In the pre-vaccine era, serotypes not contained in PCV7 (VRS or NVS) show a lower rate of penicillin or erythromycin resistance than VS. Both international clones and newly-described clones were detected and capsular switching was observed. Future monitoring of serotypes and clones in the vaccine era is of paramount importance.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Subject:
Location: ICC, Munich, Germany
Presentation type:
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