We studied the etiology of bronchiolitis in Delhi. Respiratory syncytial virus (RSV) was the most commonly isolated virus in 72/245 infants (30%). RSV positive cases did not have more severe disease; this argues against routine use of ribavirin.

Key words: Bronchiolitis, Delhi, Respiratory syncytial virus.

There are numerous studies looking at the etiology of bronchiolitis in the West but few from the tropics(1-4), with only one study from India(5).

We conducted this trial in a Delhi hospital between January 1 and December 31, 2007 and enrolled 245 infants (1 month to 1 year) with evidence of bronchiolitis (characterized by tachypnea; respiratory rate more than 60 per minute between 1-2 months of age and more than 50 per minute beyond 2 months age; with wheezing or fine crackles) following a written informed consent from parents. Nasopharyngeal aspirates, nasopharyngeal swabs and throat swabs were obtained from them and evaluated at the National Institute of Communicable Diseases (NICD), Delhi. Specimens were processed for viral culture, ELISA and PCR. The study was approved by the hospital research committee.

Viral identification rate was 46.12%. Respiratory syncytial virus (RSV) was isolated in 72 (29.38%) cases, adenovirus in 19 (7.75%), influenza virus in 3 (1.22%) (Type A: 1 and Type B: 2), parainfluenza virus in 9 (3.67 %) (type 1: 7 cases and type 3 : 2 cases), rhinovirus in 6 (5.31%) and metapneumo-virus in 1 (0.88%). Mixed infections were documented in 6.6% of cases.

RSV was most commonly isolated in November. The incidence peaked in the early part of winter, similar to the pattern seen in the West.

We tried to correlate the clinical profile of cases with the virus isolated. We found fever, fever with crepitation, and fever with crepitation and rhonchi, significantly more associated with RSV compared to infants without RSV (P value 0.015, 0.024 and 0.016, respectively). Unlike(6), El Radhi, et al. we did not find an association of fever with more severe illness.

Although a higher severity of illness and fatality rates in bronchiolitis with adenovirus(7) and rhinovirus(8) have been reported previously, we found no statistical association between the virus identified and severity of illness (defined as a Downe’s respiratory distress score of 4 or more, for purposes of this study).

Antiviral treatment with ribavirin is not prescribed in the West, except in the most serious cases. In the present study, RSV was not isolated in 70% cases and its isolation was not associated with more severe disease. This argues against routine use of ribavirin in bronchiolitis. More studies need to be done from other parts of the country to look for regional differences in incidence and etiology.