Epidemiology of viral respiratory infections and the kinetics of influenza and RSV antibodies among Navajo and White Mountain Apache infants from birth to 6 months

Angelia A. Eick
School of Public Health, John Hopkins University
July, 2006


American Indian infants have significantly higher rates of acute respiratory infections compared to the general US population (ARI). To better understand the epidemiology and etiology of these high rates of ARI among Navajo and White Mountain Apache infants less than 6 months of age, we conducted three separate analyses. For aims 1 and 3, maternal post-partum, infant cord, 2-3 month and 6 month serum were collected and assayed for influenza HI antibodies. Nasal aspirates were obtained for ARI through 6 months of age; cell culture was used to identify viral infections. For aim 2, cord blood specimens were collected and assayed for neutralizing RSV antibody. Hospitalized infants with a respiratory illness had a nasal aspirate collected and tested for RSV. For aim1, we found that RSV, rhinovirus, and influenza were the most frequent viruses isolated for ARI. The RSV incidence and hospitalization rates were 4 times that of the general US population, 236.5 and 132.2 per 1000 person-years, respectively. The incidence of rhinovirus and influenza were 2 times that of the general US population, 229.6 and 34.8 per 1000 person-years, respectively. For aim 3, we found that infants of immunized mothers had significantly higher influenza HI antibody titers from birth to 2-3 months of age for all 5 influenza subtypes investigated as compared to infants of un-immunized mothers (p?0.0001). The transplacental transfer ratio was 1.24-1.36 for immunized mother/infant pairs and 1.15-1.27 for un-immunized mother/infant pairs. The matched RSV case-control analysis used in aim 2 found that for every 1 natural log increase in cord blood RSV neutralizing antibodies there was a 30% reduced risk of hospitalization with RSV (OR = 0.69, P=0.003). These findings confirm the high rates of ARI among this population for both inpatient and outpatient ARI. We found the etiology of these high rates is not due to a lack of RSV or influenza maternal antibodies or a low transplacental transfer rate. These findings support the significant need for tools to prevent respiratory infections in this high risk population and give insight to better tailor ARI prevention strategies for this population.