Pneumococcal carriage in children during their first two years: important role of family exposure.
BACKGROUND
Close family and day-care contacts have been identified as risk factors for pneumococcal (Pnc) carriage. This study addresses the risk of Pnc carriage by infants 2 to 24 months of age in terms of simultaneous carriage of pneumococcus by family members.


METHODS
Nasopharyngeal swabs were collected from 100 Finnish infants and their family members on 10 scheduled visits (when infant was 2, 3, 4, 5, 6, 9, 12, 15, 18 and 24 months of age). The 7 most common pneumococcal serogroups (4, 6, 9, 14, 18, 19, 23), also represented in the new heptavalent Pnc conjugate vaccine, were analyzed. Marginal logistic regression analyses were performed to assess the relative importance of different predictors for carriage.


RESULTS
The carriage of the studied Pnc serogroups increased with age, being highest at the age of 18 months (28%). Among children older than 6 months of age, the strongest predictor of carriage was simultaneous carriage of the same serogroup by another family member (odds ratio, 3.8; 95% confidence interval, 2.1 to 6.9). At the age of 6 months or younger, carriage was rare and was not significantly associated with a family carriage.


CONCLUSIONS
Young infants (< or =6 months old) were largely protected from pneumococcal carriage. After this age family transmission seemed very important despite the small family size. Contrary to some earlier studies communal day care was not associated with an increased risk of Pnc carriage. This could be partly because of the long parental leave in Finland and thus the late age of starting organized day care.
Leino
T
T
Department of Vaccines, National Public Health Institute, Helsinki, Finland. tuija.leino@ktl.fi
Auranen
K
K
Jokinen
J
J
Leinonen
M
M
Tervonen
P
P
Takala
A K
AK
D000367:Age Factors; D002353:Carrier State / Q000453:epidemiology* / Q000635:transmission; D002656:Child Day Care Centers; D015331:Cohort Studies; D018562:Disease Transmission, Infectious; D005191:Family Characteristics; D005192:Family Health; D005260:Female; D005387:Finland / Q000453:epidemiology; D006801:Humans; D007223:Infant; D008297:Male; D009305:Nasopharynx / Q000382:microbiology; D016017:Odds Ratio; D011008:Pneumococcal Infections / Q000453:epidemiology* / Q000209:etiology / Q000635:transmission; D012307:Risk Factors; D012703:Serotyping; D013296:Streptococcus pneumoniae / Q000145:classification / Q000302:isolation & purification*