Nine studies were included: 4 prospective studies and 5 retrospective studies. The total number of participants was 33,211 (26,692 in the prospective studies and 6,519 in the retrospective studies).
The mean quality score was 17.4 for the prospective studies and 14.6 for the retrospective studies. No further details were reported.
A total of 12,082 participants and 1,817 asthma cases were included in the analysis of the risk of asthma following at least one course of antibiotics. A meta-analysis of 3 prospective studies (5,563 participants) showed no significant difference in the risk of asthma due to antibiotic exposure in the first year of life between exposed and non-exposed groups (unadjusted OR 1.12, 95% CI: 0.88, 1.42). The 5 retrospective studies (6,519 participants) showed an increased risk with antibiotic exposure that was statistically significant (OR 2.82, 95% CI: 2.07, 3.85, p=0.04), as did the pooled analysis of all 9 studies (OR 2.05, 95% CI: 1.41, 2.99, p<0.01). There was statistically significant heterogeneity between the retrospective studies. The subgroup comparison found no significant difference between the 3 studies in high-risk populations and those in the general population.
A total of 27,167 participants and 3,392 asthma cases were included in the dose-response analysis. Three prospective studies (25,755 participants) and 2 retrospective studies (1,412 participants) were included in the meta-analysis. Overall, there was no statistically significant difference in the OR for the risk of asthma for each additional course of antibiotics taken in the first year of life. Heterogeneity between the studies was statistically significant. The pooled OR from the 2 retrospective studies showed a significantly higher risk of asthma and no evidence of statistical heterogeneity.
The 'influence analysis' unsurprisingly showed that removal of individual studies from the meta-analyses could change the effect size and degree of heterogeneity.
There was no evidence of publication bias, although the analysis was limited by the small number of studies.