Background and aims To evaluate the use of antibiotics and its relation to the length of stay (LOS) in patients hospitalised with acute bronchiolitis (AB).

Patients and Method In a context of a randomised, controlled, double-blind clinical trial, 177 infants hospitalised with AB in two epidemics (2011–2013) were included. They were classified according to the scale of Wood- Downes modified by Ferres (WDF), in mild (MiB), moderate (MB) or severe (SB). The primary outcome was LOS. We evaluated the antibiotic used and CRP. Data were analysed with SPSS17.

Results There were 7.9% MiB, 83.6% MB and 8.5% SB. Of them, 21.4% of MiB, 14.2% of MB and 66.7% of the SB received antibiotic therapy. The most commonly used antibiotics were amoxicillin-clavulanate, cefotaxime and azithromycin. The most frequent reasons were clinical worsening measured by WDF scale, increased CRP and fever. The mean LOS for acute bronchiolitis without antibiotics was 4.51 days and with antibiotics 7.84 days (p = 0.001). The use of antibiotics in SB was significantly higher than in MB (p = 0.001). In the group of MB, the mean LOS was 4.44 days (no antibiotics) vs 7.29 (antibiotics), p = 0.001. In the group of BG, the mean LOS was 9.4 days vs. 13.5 days, p = 0.53. There were statistically significant differences in elevated CRP and the use of antibiotics (p = 0.005).

Conclusions The AB who received antibiotics had significantly more LOS. There were statistically significant differences to received antibiotics in MB, but not in SB, perhaps because the LOS of this group is high.