Eighteen Years of Respiratory Syncytial Virus Surveillance
Eighteen Years of Respiratory Syncytial Virus Surveillance
Background: Alaska Native infants from the Yukon-Kuskokwim Delta (YKD) experienced respiratory syncytial virus (RSV) hospitalization rates 5 times higher and an RSV season twice as long as the general US infant population. We describe trends in hospitalization rates and seasonality during 18 years of continuous RSV surveillance in this population and explore contributions of climate and sociodemographic factors.
Methods: We abstracted clinical and RSV test information from computerized medical records at YKD Regional Hospital and Alaska Native Medical Center from 1994 to 2012 to determine hospitalization rates and RSV season timing. Descriptive village and weather data were acquired through the US Census and Alaska Climate Research Center, University of Alaska, Fairbanks, respectively.
Results: During 1994–2012, YKD infant RSV hospitalization rates declined nearly 3-fold, from 177 to 65 per 1000 infants/yr. RSV season onset shifted later, from mid October to late December, contributing to a significantly decreased season duration, from 30 to 11 weeks. In a multivariate analysis, children from villages with more crowded households and lacking plumbed water had higher rates of RSV hospitalizations (relative rate, 1.17; P = 0.0005 and relative rate, 1.45; P = 0.0003). No association of temperature or dew point was found with the timing or severity of RSV season.
Conclusions: Although the RSV hospitalization rate decreased 3-fold, YKD infants still experience a hospitalization rate 3-fold higher than the general US infant population. Overcrowding and lack of plumbed water were associated with RSV hospitalization. Dramatic changes occurred in RSV seasonality, not explained by changes in climate.
Lower respiratory tract infections (LRTI) are the number one cause of death globally in children outside of the neonatal period, and respiratory syncytial virus (RSV) infection is a major cause of LRTI worldwide. In the US, RSV is the most frequent cause of hospitalization for infants, with a hospitalization rate during 1993–2008 of 23 per 1000 children younger than 1 year old, although some prospective studies report half that rate. The burden of RSV LRTI infection in young children disproportionately affects Alaska Native (AN) children, and the reported RSV hospitalization rate for AN infants from the remote Yukon-Kuskokwim Delta (YKD) region of Alaska is 5 times higher than in the US general population. Compared with RSV hospitalization rates around the world, this rate is surpassed only by the Canadian Inuit, at 166 per 1000 infants.
Using YKD surveillance data, we have previously shown that RSV epidemiology was characterized by a prolonged RSV season (30.5 weeks compared with 15 weeks for the US). The seasonality of RSV is an inherent characteristic of this infection. In temperate climates, RSV activity peaks in the winter months, whereas tropical areas have a prolonged continuous season with overall lower rates of RSV. Anticipating the timing of the RSV season is important for cost-efficient use of palivizumab prophylaxis. Seasonality is likely determined by weather and socio- environmental effects, which alter virus infectivity or host susceptibility, and affects social patterns, such as promoting indoor cohabitation, which can increase RSV transmission. Social factors are important determinants of health in YKD; prior studies documented high rates of household crowding, lack of running water and woodstove use, which have all been associated with increased risk of RSV or LRTI hospitalization.
We analyzed 18 years of surveillance data for LRTI and RSV hospitalization in children younger than 3 years old living in YKD, an isolated population with a single health-care system, to evaluate trends in hospitalization rates and RSV seasonality over time. We looked at the relationship of climate factors to RSV season timing. We evaluated the contribution of village-level demographic characteristics to risk of RSV infection.
Abstract and Introduction
Abstract
Background: Alaska Native infants from the Yukon-Kuskokwim Delta (YKD) experienced respiratory syncytial virus (RSV) hospitalization rates 5 times higher and an RSV season twice as long as the general US infant population. We describe trends in hospitalization rates and seasonality during 18 years of continuous RSV surveillance in this population and explore contributions of climate and sociodemographic factors.
Methods: We abstracted clinical and RSV test information from computerized medical records at YKD Regional Hospital and Alaska Native Medical Center from 1994 to 2012 to determine hospitalization rates and RSV season timing. Descriptive village and weather data were acquired through the US Census and Alaska Climate Research Center, University of Alaska, Fairbanks, respectively.
Results: During 1994–2012, YKD infant RSV hospitalization rates declined nearly 3-fold, from 177 to 65 per 1000 infants/yr. RSV season onset shifted later, from mid October to late December, contributing to a significantly decreased season duration, from 30 to 11 weeks. In a multivariate analysis, children from villages with more crowded households and lacking plumbed water had higher rates of RSV hospitalizations (relative rate, 1.17; P = 0.0005 and relative rate, 1.45; P = 0.0003). No association of temperature or dew point was found with the timing or severity of RSV season.
Conclusions: Although the RSV hospitalization rate decreased 3-fold, YKD infants still experience a hospitalization rate 3-fold higher than the general US infant population. Overcrowding and lack of plumbed water were associated with RSV hospitalization. Dramatic changes occurred in RSV seasonality, not explained by changes in climate.
Introduction
Lower respiratory tract infections (LRTI) are the number one cause of death globally in children outside of the neonatal period, and respiratory syncytial virus (RSV) infection is a major cause of LRTI worldwide. In the US, RSV is the most frequent cause of hospitalization for infants, with a hospitalization rate during 1993–2008 of 23 per 1000 children younger than 1 year old, although some prospective studies report half that rate. The burden of RSV LRTI infection in young children disproportionately affects Alaska Native (AN) children, and the reported RSV hospitalization rate for AN infants from the remote Yukon-Kuskokwim Delta (YKD) region of Alaska is 5 times higher than in the US general population. Compared with RSV hospitalization rates around the world, this rate is surpassed only by the Canadian Inuit, at 166 per 1000 infants.
Using YKD surveillance data, we have previously shown that RSV epidemiology was characterized by a prolonged RSV season (30.5 weeks compared with 15 weeks for the US). The seasonality of RSV is an inherent characteristic of this infection. In temperate climates, RSV activity peaks in the winter months, whereas tropical areas have a prolonged continuous season with overall lower rates of RSV. Anticipating the timing of the RSV season is important for cost-efficient use of palivizumab prophylaxis. Seasonality is likely determined by weather and socio- environmental effects, which alter virus infectivity or host susceptibility, and affects social patterns, such as promoting indoor cohabitation, which can increase RSV transmission. Social factors are important determinants of health in YKD; prior studies documented high rates of household crowding, lack of running water and woodstove use, which have all been associated with increased risk of RSV or LRTI hospitalization.
We analyzed 18 years of surveillance data for LRTI and RSV hospitalization in children younger than 3 years old living in YKD, an isolated population with a single health-care system, to evaluate trends in hospitalization rates and RSV seasonality over time. We looked at the relationship of climate factors to RSV season timing. We evaluated the contribution of village-level demographic characteristics to risk of RSV infection.
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