Sexually Transmitted Diseases

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Sexually Transmitted Diseases:

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‡

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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.

© Copyright 2005 American Sexually Transmitted Diseases Association


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