Background:
In 2003, only 28 of Michigan's 83 counties had a gonorrhea (GC) prevalence rate of over 1% among specimens submitted to the Michigan Regional Laboratory System (MRL). At this time, all specimens submitted to MRL for chlamydia (CT) testing were tested simultaneously for GC.
Considering the low positive predictive value of nucleic acid amplification tests for GC in low-prevalence jurisdictions, and the potential cost savings associated with the CT- only test, Michigan adopted a CT-only testing algorithm. Under the algorithm, counties with GC prevalence of < 1% in public sites were designated for CT-only testing. A positive CT result automatically triggered GC testing of the same specimen in these areas.

Objective:
To describe the impact of CT-only testing on disease prevalence and IPP costs in Michigan.

Method:
Two Michigan Bureau of Laboratory data sets, one containing GC and CT screening test results, and another containing screening provider data, were merged in SAS by a unique provider code. Frequencies were analyzed, and significance was tested using Pearson's Chi-Square Test.

Result:
In 2003, 83,140 combined CT/GC tests were performed in Michigan's publicly funded IPP sites. Two thousand fifty-two (2,052), or 2.9% were positive for GC. In 2006, following the implementation of the CT-only algorithm the number of specimens tested for GC decreased 5% to 78,818. Among these tests, 4,094 cases (5.2% positivity) of GC were identified, an increase of 67% from 2003 (p<0.00001). During the same time period, the number of specimens tested for CT increased 20% from 82,681 in 2003 to 98,698 in 2006. Positivity increased from 8.6 to 10.3% (p<0.00001).

Conclusion:
Utilizing the CT-only test for specimens from low prevalence jurisdictions increased the availability of testing and detected more positives while holding program costs in check.

Implications:
Other states with distinct areas of low and high prevalence may choose to implement the CT-only testing algorithm.