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Reassessing a Large-Scale Syphilis Epidemic Using an Estimated Infection Date

Schumacher, Christina M. MHS*; Bernstein, Kyle T. PhD; Zenilman, Jonathan M. MD; Rompalo, Anne M. MD, ScM

doi: 10.1097/01.olq.0000175400.40084.3e
Article

Objectives: Timely ascertainment of syphilis cases is critical to initiating disease-control measures. Epidemic curves typically use the report date and may introduce lag-time bias into assessment.

Goal: To reassess a large syphilis epidemic using an imputed infection date.

Study: We compared 2 types of epidemic curves—1 based on report date and 1 on estimated infection date—using the large 1993–2003 Baltimore epidemic as our model.

Results: In general, the shape of the report curves did not accurately reflect the shape of the corresponding infection curves during the growth period (period of largest increase in incidence); during the hyperendemic period (period of highest incidence), peaks in report curves did not follow peaks in the infection curve by the appropriate lag time. There was a tendency for reporting data to underestimate infections during the growth period and overestimate infections during the hyperendemic period. A sensitivity analysis showed similar trends regardless of the length of stage-specific incubation period used.

Conclusions: Lag-time bias may be present when using epidemic curves based on report dates. Health departments should consider using an estimated infection date.

Reassessment of a large-scale syphilis epidemic found that epidemic curves based on estimated infection date may better describe epidemics than traditionally derived report date curves.

From the *Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland; †Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, and Baltimore City Health Department, Baltimore, Maryland; and the ‡Johns Hopkins University School of Medicine, Division of Infectious Diseases, Baltimore, Maryland

This work was supported by NIH grants R01-AI45724 and K24-AI01633.

The authors would like to thank Vivian Go, Laura McGough, and Aaron Goodfellow for their insightful comments on and corrections to the manuscript.

Address for reprints: Anne M. Rompalo, MD, ScM, 1830 East Monument Street, Room 447, Baltimore, MD 21205. E-mail: arompalo@jhmi.edu.

Received for publication June 4, 2004, and accepted April 4, 2004.

© Copyright 2005 American Sexually Transmitted Diseases Association