Background: Respiratory syncytial virus (RSV) is a common cause of lower respiratory tract infection in children younger than one year. It is estimated that 44 percent of children in the United States receive medical attention for RSV infection in the first year of life, and 95 percent of those are treated by their primary care physician or in an emergency department. About 40 percent of children who are infected develop recurrent wheeze; therefore, RSV results in significant medical costs and reduces health-related quality of life.

Known risk factors for RSV include prematurity, young age, male sex, heart and lung disease, Down syndrome, no or limited breastfeeding, presence of siblings, day care attendance, and exposure to tobacco smoke. Clinical prediction rules have been developed to predict the need for hospitalization of preterm infants, but not for healthy term infants likely to be treated as outpatients. Because RSV can be prevented with risk-factor modification, Houben and colleagues developed a clinical prediction rule to identify healthy term infants at high risk of RSV lower respiratory tract infection in the first year of life.

The Study: Two large urban hospitals in the Netherlands invited all term newborns (at least 38 weeks' gestation) without major congenital anomalies to participate in a prospective birth cohort study. Of 1,080 eligible newborns, 341 (32 percent) participated in the study. Parents who declined to participate commonly cited the protocol that required daily measurement collection. Baseline characteristics were similar in participants and nonparticipants. At the onset of any respiratory episode, parents recorded their child's daily respiratory symptoms, including cough and wheeze, and obtained nasal/throat swabs. Lower respiratory tract infection was strictly defined as moderate or severe cough or any wheeze for two or more days. The presence of risk factors was ascertained from hospital birth records (sex, gestational age, birth weight, and birth month), and from parental questionnaires completed when the children were one month and one year of age.

The primary outcome was the diagnosis of RSV lower respiratory tract infection, determined by clinical symptoms and the presence of RSV RNA detected from polymerase chain reaction of the swabs sent in by parents. Secondary outcomes included RSV lower respiratory tract infections requiring primary care attention, the prevalence of wheeze in the first year, and the impact of wheeze on the child's health-related quality of life as determined by responses to a preschool quality-of-life questionnaire. The association between each risk factor and the presence or absence of RSV lower respiratory tract infections was analyzed through univariate regression; risk factors predictive of RSV were included in multivariate regression analysis. Factors most related to developing RSV were included in the prediction rule. Individual scores were determined by assigning points for each variable and adding the results.

Results: Of the 298 newborns with complete data, 42 (14 percent) developed RSV lower respiratory tract infections. Of these 42 newborns, 27 (64 percent) visited a primary care physician and three were hospitalized. The final reduced regression model included four independent predictive variables: day care attendance and/or the presence of older siblings (two points); high parental education levels (one point); birth weight greater than 8 lb, 13 oz (4 kg; one point); and birth date between April and September (one point). Children at lowest risk (score of 0 to 2) had an absolute risk of developing RSV of 3 percent, whereas children at highest risk (score of 5) had an absolute risk of 32 percent. The authors theorized that parents with a higher education level may seek medical care earlier to obtain a formal diagnosis. The authors also suggested that a larger birth weight may be associated with a longer labor and altered immunity. Children diagnosed with RSV were twice as likely to wheeze during the first year of life as children who were not infected (62 versus 36 percent; P = .003), and they visited a physician more often for respiratory problems (48 versus 30 percent; P = .03).

Conclusion: This clinical prediction rule identifies children at the highest and lowest risks of RSV lower respiratory tract infections, which can help target preventive and monitoring strategies.