Effect of the seven-valent conjugate pneumococcal vaccine on carriage and drug resistance of Streptococcus pneumoniae in healthy children attending day-care centers in Lisbon.
OBJECTIVE
Prospective study to evaluate the impact of the 7-valent pneumococcal conjugate vaccine (Prevenar) on the nasopharyngeal (NP) carriage of drug-resistant Streptococcus pneumoniae (DRPn), by healthy children attending day-care centers (ages 6 months-6 years).


METHODS
Vaccinees (238 children) who received vaccine and controls (457 children) were followed for carriage of total S. pneumoniae and DRPn and for the serotypes and genetic backgrounds of DRPn during 6 consecutive sampling periods between May 2001 and February 2003.


RESULTS
We detected no significant differences between vaccinees and the control group in the total carriage rate of Pn (average, 68%) or in the frequency of carriage of DRPn (average, 38%), including the frequency of penicillin-nonsusceptible strains (average, 24%). In contrast, there was a decline in the carriage of DRPn with vaccine serotypes which was compensated by the appearance and gradual increase in the frequency of DRPn expressing unusual serotypes (6A, 10A, 15A and 15C, 19A, 23A, 33F) which were not present in the vaccine as well as an increase in nontypable strains. The majority of the DRPn with unusual serotypes showed different pulsed field gel electrophoresis patterns indicating replacement of the original resistant flora by other clonal types of drug-resistant bacteria. Antibiotic consumption and the frequency of respiratory tract infections were similar among the vaccinees and controls.


CONCLUSIONS
Pneumococcal vaccination did not change the frequency of carriage of drug-resistant strains being the initially dominant vaccine serotypes replaced by others expressing nonvaccine serotypes. Reduction in the carriage of DRPn may require a combination of the conjugate vaccine and a decrease in antibiotic pressure.
Frazão
Nelson
N
Laboratory of Molecular Genetics, Instituto de Tecnologia Química e Biológica da Universidade Nova de Lisboa, Lisboa, Portugal.
Brito-Avô
António
A
Simas
Carla
C
Saldanha
Joana
J
Mato
Rosario
R
Nunes
Sónia
S
Sousa
Natacha G
NG
Carriço
João A
JA
Almeida
Jonas S
JS
Santos-Sanches
Ilda
I
de Lencastre
Hermínia
H
D017677:Age Distribution; D002353:Carrier State / Q000453:epidemiology / Q000276:immunology*; D016022:Case-Control Studies; D002656:Child Day Care Centers; D002675:Child, Preschool; D024881:Drug Resistance, Bacterial; D005260:Female; D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D006801:Humans; D015994:Incidence; D008297:Male; D022401:Meningococcal Vaccines / Q000008:administration & dosage* / Q000276:immunology; D009305:Nasopharynx / Q000382:microbiology; D011008:Pneumococcal Infections / Q000453:epidemiology / Q000276:immunology* / Q000517:prevention & control*; D022242:Pneumococcal Vaccines / Q000008:administration & dosage* / Q000276:immunology; D011174:Portugal / Q000453:epidemiology; D011336:Probability; D012016:Reference Values; D012307:Risk Factors; D012494:Sampling Studies; D017678:Sex Distribution; D013296:Streptococcus pneumoniae / Q000276:immunology* / Q000302:isolation & purification; D014505:Urban Population; D018074:Vaccines, Conjugate / Q000008:administration & dosage / Q000276:immunology
D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D022401:Meningococcal Vaccines; D022242:Pneumococcal Vaccines; D018074:Vaccines, Conjugate