Why are inner-city babies more prone to asthma?

Babies born into low-income, urban environments develop wheezing illnesses and asthma more often than suburban infants, and these findings have prompted research to identify the viral pathogens that lead to asthma or indicate predisposition to the disease.

Researchers suspected that exposure to allergens from cockroaches and mice, indoor and outdoor pollutants, stress, diet, and genetics led to virus-induced wheezing illnesses in urban infants and that these babies would demonstrate unique patterns of infection with respiratory viruses that place them at risk for developing asthma.

They compared the etiologies of viral respiratory illnesses in 515 infants from 4 inner-city areas (Boston, Baltimore, St. Louis, and New York City) with 285 infants from suburban Madison, Wisconsin. All the infants had a family history of allergy or asthma. The investigators collected nasal mucus specimens from study participants during respiratory illnesses and again when the infants were aged 1 year. Samples were analyzed for common viruses using cultures, immunofluorescent antibody staining, and polymerase chain reaction testing.

The babies from the urban sites had lower rates of virus detection for human rhinovirus and respiratory syncytial virus and higher rates of adenovirus infection compared with babies from the suburban group. Nearly 5% of infants from all 4 urban locations tested positive for adenovirus alone compared with 0.7% of suburban infants.

Data for low viral detection rates in urban infants suggest that inner-city infants were more likely than suburban infants to have respiratory illnesses caused by bacterial infection such as Streptococcus pneumoniae and Haemophilus influenzae or noninfectious illnesses caused by exposure to pollutants or other noxious environmental stimuli.

The researchers note that adenoviruses cause respiratory symptoms, colds, bronchiolitis, lower respiratory tract illness, gastroenteritis, and keratoconjunctivitis. Persistent infections with adenovirus over weeks or months could affect infants’ developing lungs and immune systems, leading to long-term changes.

They plan to follow the urban infants until they are aged 7 years to see whether chronic adenovirus infection is associated with increased rates for asthma and reduced lung function.

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