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Premature birth increases infants' risk of hospitalization and complications from respiratory syncytial virus

Respiratory syncytial virus (RSV) can cause bronchiolitis and pneumonia, which are major reasons for infant hospitalizations in the United States each year. Premature infants of 33 to 35 weeks gestational age (GA) are at much greater risk than term infants for severe RSV outcomes, according to a study supported by the Agency for Healthcare Research and Quality (contract 290-95-0042) and led by Susan D. Horn, Ph.D., of the Institute for Clinical Outcomes Research. A second study by the same group found that complications were common in infants hospitalized for bronchiolitis or RSV pneumonia, were more common among premature infants, and were associated with longer stays and higher costs. Both studies are summarized here.

Horn, S.D., and Smout, R.J. (2003, November). "Effect of prematurity on respiratory syncytial virus hospital resource use and outcomes." Journal of Pediatrics 143, pp. S133-S141.

In this study, the investigators analyzed medical record data for 304 infants aged 1 year or less who were admitted to one of nine children's hospitals in 1995 and 1996 for bronchiolitis or RSV pneumonia. They compared resource use—for example, intensive care unit (ICU) admission, intubation, and hospital and ICU length of stay—and outcomes of 215 term infants (GA 37 weeks or longer) with 89 infants with a GA less than 37 weeks (divided into three subgroups: 32 weeks or less, 33 to 35 weeks, and 36 weeks).

Infants who were 36 weeks GA had outcomes similar to term infants. However, after controlling for factors such as severity of illness and site-level medical practice variations in intubation and ICU admission rates, infants with a GA of 33 to 35 weeks had hospital and ICU lengths of stay greater than those of any other GA group and significantly higher intubation rates. This is the first multicenter study of laboratory-confirmed RSV hospitalizations to demonstrate that infants born at 33 to 35 weeks GA have hospital resource use at least as great as infants of 32 weeks GA or less.

True alveoli (small air sacs in the lung) begin to form between 32 and 35 weeks GA, with all infants having alveoli by 36 weeks GA. Premature birth during this critical period of lung development (32-35 weeks GA) may result in significant alteration in lung function and physiology, explain the researchers. Their study also confirmed an independent effect of prematurity beyond that caused by severity of illness and many other confounding variables (including bronchopulmonary dysplasia and heart disease).

Willson, D.F., Landrigan, C.P., Horn, S.D., and Smout, R.J. (2003, November). "Complications in infants hospitalized for bronchiolitis or respiratory syncytial virus pneumonia." Journal of Pediatrics 143, pp. S142-S149.

Complications are common in infants hospitalized for bronchiolitis or RSV pneumonia, and they are associated with longer pediatric intensive care unit (PICU) and hospital stays and higher costs. However, infants born prematurely and those with congenital abnormalities are at significantly greater risk for complications, according to this study. The investigators analyzed medical record data on 684 infants 1 year old or younger with bronchiolitis or RSV pneumonia who were admitted to 10 children's hospitals in 1995 and 1996. They examined complication rates and their effects on hospital and PICU length of stay and hospital costs.

Most infants (79 percent) had one or more complications, with serious complications affecting 24 percent. Even minor complications were associated with significantly longer PICU and hospital stays and higher costs. Respiratory complications were most frequent (60 percent), but infectious (41 percent), cardiovascular (9 percent), electrolyte imbalance (19 percent), and other complications (9 percent) were common.

Complication rates were higher in infants born prematurely (87 percent), infants with congenital heart disease (93 percent), and infants with other congenital abnormalities (90 percent) relative to infants without risk factors (76 percent). Infants 33 to 35 weeks GA had the highest complication rates (93 percent), as well as longer hospital stays and higher costs than other premature infants. The researchers suggest that broader use of RSV prevention be considered for these high-risk infants.

Editor's Note: Another AHRQ study on a related topic found that breastfeeding reduces by half the risk of neonatal respiratory tract infection among newborn girls but not boys. For more details, see: Sinha, A., Madden, J., Ross-Degnan, D., and others (2003, October). "Reduced risk of neonatal respiratory infections among breastfed girls but not boys." (AHRQ grant HS10060). Pediatrics 112(4), pp. e303-e307.

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