Original ResearchDensity of day cares in relation to reported pertussis incidence in Philadelphia
Introduction
With parental shifts in employment over the last few decades, day care enrollment as well as the number of facility options in a community have both increased.1 Within these day care facilities, children, teachers, and parents congregate, providing an opportunity for transmission of highly contagious diseases. In a study undertaken by the National Institute of Child Health and Human Development investigators observed a direct link between the rates of communicable disease and use of out-of-home child care,2 and a follow-up study demonstrated the risk is magnified based on the number of children in the day care.3 The recent increase in respiratory infectious diseases, such as pertussis, may be partially attributable to this occurrence, especially if the children are unimmunized or underimmunized.4, 5 Vaccination against pertussis, a multi-dose series started around two months of age and completed by age six years, means that children enrolled in day cares at younger ages have potentially vulnerable immune systems, as the full series may not be completed. Although some immunologic benefit occurs from receiving fewer doses, optimal protection is conferred from completion of the primary series.6
A review of vaccine-preventable infectious diseases in day cares noted that the average age of children enrolled in day care was decreasing, while immunization coverage was increasing.7 Yet two recent studies found evidence that pertussis outbreaks can occur in these congregant settings despite high vaccination coverage, and further that vaccinated children can be asymptomatic carries of the pathogen.8, 9 While literature is scant on the relationship between day care attendance and pertussis, these two studies from Israel underscore the importance of not only proper vaccination for children and adults within the day care environment, but also protection for the community at large as these children interact within their neighborhoods.
Few studies have been conducted that consider day care attendance as the primary exposure and pertussis as the outcome, and to our knowledge no study has examined the relationship between prevalence of day care facilities and community risk of disease. This disease is of particular interest as there has been a sharp increase in cases over recent years. To demonstrate a correlation between day care use and community infection, the key assumption is that the community uses local day care. A 2013 review of child care decision making processes noted both ‘accessibility of providers is […] a strong correlate of child care choices’ and travel beyond the local community for day care was often ‘unmanageable,’ particularly for low income families.10 One potential measure of accessibility is through a day care density metric, which allows for neighborhoods with more day cares per area to have a higher level of exposure. This implies potential for increased use by the local residents and more sources for pathogen transmission. In this study, we sought to examine the interplay between Philadelphia neighborhood and pertussis risk, with specific focus on day cares as the risk factor of interest. Our hypothesis was that neighborhoods with a greater density of day cares would report a greater number of incident pertussis cases to the local Health Department.
Section snippets
Source population and study sample
Two data sources served as the source population for this study: the clinical disease management system (CDMS) and the Philadelphia immunization information system (IIS) dubbed KIDS Plus. CDMS logs and tracks all notifiable diseases reported to the Philadelphia Department of Public Health (PDPH) as mandated by the Philadelphia Health Code.11 KIDS Plus provides a lifetime snapshot of immunization history, is linked to a variety of other systems including vital records to provide other health
Results
The study sample included 2050 children aged birth through six years, residing in 45 Philadelphia neighborhoods for the years 2001 through 2013. Among these children, there were 410 cases of confirmed and probable pertussis reported to the Health Department.
Discussion
In this multilevel analysis, we examined the distribution of reported pertussis cases throughout Philadelphia between 2001 and 2013. Our main finding was a possible clustering effect corresponding to an increase risk of disease based solely on the neighborhood where one resides. Secondary findings suggest that correlates of pertussis infection in this study sample are driven by familial and individual factors rather than ecological exposures.
Determinants of infectious disease not only include
Author contributions
NDG, ECN, and SLW conceptualized the study. NDG and LPT carried out all analyses. NDG drafted the initial manuscript, and all authors approved the final version.
Acknowledgements
The authors would like to thank Caroline Johnson, Kate Drezner, and Jennifer Gutowski of the Philadelphia Department of Public Health.
A portion of this work was presented at the 2016 Epidemiology Congress of the Americas (Miami, FL).
Ethical approval
Institutional Review Board approval was obtained from the City of Philadelphia, and Drexel University.
Funding
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