Background: Chlamydia and gonorrhea are among the most commonly reported diseases in the United States. A meta-analysis showed a reinfection rate of 13.9% for chlamydia cases and 11.7% for gonorrhea cases. Distinguishing between duplicate cases and reinfections is necessary for accurate burden assessment. The Department of Defense (DOD) performs routine public health surveillance for these conditions. The DOD and other public health entities use differing methods to assess disease burden. Comparison is necessary to assess impact of varying methods and ensure proper data source utilization.
Methods: Within the DOD, the two most common methods used to identify unique infections are the 30 day running clock method and the 30 day gap in care method. The 30 day running clock method considers any diagnosis or positive test within 30 days of an original record as the same case. The 30 day gap in care rule requires 30 days without any encounter or positive test for a new case. Chlamydia and gonorrhea outpatient encounters and laboratory results identified for DOD military health system beneficiaries during 2012 were extracted. The two methods for unique case identification were compared.
Results: Most cases were not affected by the application of two different case identification methods. The use of the 30 day gap in care method reduced chlamydia cases by 0.2% and gonorrhea cases by 1.9%, as compared to the 30 day running clock method.
Conclusions: Small differences in case volume were identified when the two methods were applied to the same data. The 30 day gap in care rule has the ability to reflect clinical process and is essential to an accurate assessment of disease burden. The 30 day running clock method may overestimate the burden and not adequately assess the impact of reinfections.