Thirteen RCTs (n=3,159) were included.
All of the included studies were double-blinded and of a high quality (Jadad score 4 or 5). Most of the studies had high rates of follow-up (median 94%).
Natural history (placebo groups only).
The complete clinical cure rate was 8% (95% CI: 5, 14) at 3 to 5 days, rising to 35% (95% CI: 24, 48) at 7 to 12 days and 45% (95% CI: 23, 70) at 14 to 15 days.
The improvement rate was 30% (95% CI: 0, 99) at 3 to 5 days, rising to 73% (95% CI: 56, 85) at 7 to 12 days; this remained stable at 14 to 15 days.
Clinical cure.
There was no significant difference between antibiotics and placebo in the clinical cure rate at 3 to 5 days (3 homogeneous studies) or at 14 to 15 days (4 studies with low heterogeneity, I-squared 27%). At 7 to 12 days, antibiotics were associated with a significant increase in clinical cure rates compared with placebo (absolute RD 0.15, 95% CI: 0.04, 0.25, p=0.007), based on 9 studies with high heterogeneity (I-squared 80%).
Clinical improvement.
There was no significant difference between antibiotics and placebo in clinical improvement rates at 3 to 5 days (2 heterogeneous studies, I-squared 65%). Antibiotics were associated with a significant increase in clinical improvement rates compared with placebo at 7 to 12 days (absolute RD 0.14, 95% CI: 0.01, 0.28, p=0.037), based on 5 studies with high heterogeneity (I-squared 74%), and at 14 to 15 days (absolute RD 0.07, 95% CI: 0.02, 0.13, p=0.013), based on 3 studies with low heterogeneity (these reported results were taken from the tables, but the text stated that there was no significant difference between treatments at 14 or 15 days and that the results were based on 4 studies).
Adverse events.
Antibiotics were associated with a significant increase in any adverse event (absolute RD 0.11, 95% CI: 0.05, 0.16, p=0.001; NNH 9) and a significant increase in diarrhoea, which was the most commonly reported adverse event (absolute RD 0.05, (95% CI: 0.01, 0.09, p=0.027; NNH 20), compared with placebo. Other reported adverse events were skin rashes, vaginal discharges, headaches, dizziness and fatigue.
The results for various subgroup and sensitivity analyses were also reported.