Reassessing a large-scale syphilis epidemic using an estimated infection date.
OBJECTIVE
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.


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


METHODS
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.
Schumacher
Christina M
CM
Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA.
Bernstein
Kyle T
KT
Zenilman
Jonathan M
JM
Rompalo
Anne M
AM
D015982:Bias; D018563:Disease Notification; D004196:Disease Outbreaks; D006801:Humans; D015994:Incidence; D008396:Maryland / Q000453:epidemiology; D015233:Models, Statistical; D013587:Syphilis / Q000175:diagnosis* / Q000453:epidemiology*; D013997:Time Factors