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The Timing of Pertussis Cases in Unvaccinated Children in an Outbreak Year: Oregon 2012
Steve G Robison1, Juventila Liko1
1Immunization Program, Oregon Health Authority, Portland, OR.
Insights
Unvaccinated children experienced earlier pertussis onset during the 2012 outbreak, indicating faster disease spread in these groups. This highlights the need to consider unvaccinated populations for effective outbreak control strategies.
Area of Science:
- Epidemiology
- Immunization Studies
- Public Health
Background:
- Pertussis (whooping cough) outbreaks pose a significant public health challenge, particularly in communities with varying vaccination rates.
- Understanding disease dynamics, including the timing of onset relative to vaccination status, is crucial for effective control.
Purpose of the Study:
- To determine if unvaccinated and under-vaccinated pertussis cases occurred earlier in a community during a 2012 outbreak.
- To analyze the temporal patterns of pertussis onset based on immunization status at a community level.
Main Methods:
- A 2012 pertussis outbreak in Oregon was analyzed, stratifying pediatric cases (2 months to 10 years) by immunization status, age, zip code, and onset date.
- Median onset dates were compared between fully/mostly vaccinated, poorly vaccinated, and unvaccinated groups, overall and by zip code.
- Disease clustering was assessed using SatScan analysis.
Main Results:
- Out of 351 pertussis cases, unvaccinated/poorly vaccinated children had a median onset on day 117 (April 26, 2012).
- Fully/mostly vaccinated children had a median onset 41 days later, on day 158 (June 6, 2012).
- Unvaccinated cases were 3.2 times more likely to have earlier onset dates within local zip codes compared to vaccinated cases.
Conclusions:
- Pertussis cases among unvaccinated children indicated an earlier and potentially faster spread of the disease within local areas during the outbreak.
- Effective pertussis outbreak control may necessitate targeted strategies focusing on the composition and geographic distribution of unvaccinated individuals.
Objective:
To assess whether, during a 2012 pertussis outbreak, unvaccinated and poorly vaccinated cases occurred earlier on a community level.
Study Design:
Pediatric pertussis among children 2 months to 10 years of age in the Oregon Sentinel Surveillance region during an epidemic starting at the beginning of 2012 were stratified by immunization status, age, zip code, and calendar date of disease onset. Differences in median onset as days between fully or mostly vaccinated, poorly vaccinated, and unvaccinated cases were examined overall and within local zip code areas. Disease clusters also were examined using SatScan analysis.
Results:
Overall, 351 pertussis cases occurred among children aged 2 months to 10 years of age residing in 72 distinct zipcodes. Among unvaccinated or poorly vaccinated cases, their median date of onset was at calendar day 117 (April 26, 2012), whereas for those who were fully or mostly vaccinated the median date of onset was 41 days later, at day 158 (June 6, 2012). Within each local zip code area, the unvaccinated cases were 3.2 times more likely than vaccinated cases to have earlier median dates of onset (95% CI 2.9-3.6).
Conclusion:
In this outbreak, pertussis cases among unvaccinated children represented an earlier spread of disease across local areas. Controlling outbreaks may require attention to the composition and location of the unvaccinated.
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