Background: The hygiene hypothesis suggests that higher exposure to infectious agents may be one reason for regional differences in asthma. This would suggest that immigrants from less developed countries, where infections are more common, to highly developed countries will have lower risk of asthma compared with natives, as has been found in a number of studies. We expand the research on immigrants to look at the level of development in country of origin as a predictor of asthma in New York City residents.
Methods: Data came from the 2009 cross-sectional Community Health Survey. We used logistic regression to assess the relationship of country of birth and the gross national income (GNI), an indicator of the level of development, of country of birth with asthma among immigrants and US-born New York City residents.
Results: Those who were foreign born had lower odds of having asthma compared with those US born (OR = 0.43, P < 0.001). There was a dose relationship between GNI and asthma with decreasing odds of having asthma associated with lower GNI in country of birth (low GNI country: OR = 0.26, P = 0.014; middle GNI country: OR = 0.36, P < 0.001; and high GNI country = reference).
Conclusions: These findings lend support to the hygiene hypothesis in that the odds of having asthma among New York City residents was lowest among people born in the least developed countries, as indicated by GNI, where infections are likely the most common.
Keywords: GNI per capita; asthma; hygiene hypothesis; immigrant effect.
© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.