Background:
It has been a longstanding policy in Philadelphia's STD clinic to do routine rectal cultures on women. This policy was implemented to improve casefinding in the clinic setting in consideration of the relatively low sensitivity of culture. Since NAAT (Nucleic Acid Amplification Testing) has been implemented, the utility of rectal culture to improve casefinding had not been reviewed.

Objective:
To determine whether rectal cultures for GC identified additional cases in women who had NAAT cervical testing performed. To determine whether it was cost effective to continue such testing.

Method:
An electronic review of all female patient records from Jan 2003 until Oct 2005 was conducted. All female patients with a cervical test and/or rectal culture were included.

Result:
Among 16,692 female patients who received 1 or more tests for GC (at an estimated cost of $13+ for NAAT and $0.52 for GC culture) at the time of visit, 765 (4.6%) had at least one positive result for GC. Of these, 710 (93%) had a positive GC result from NAATs cervical testing, but the other 55 (7%) were found only by rectal testing. Among these, 53 had a concomitant negative cervical test. The estimated cost to identify the additional 55 cases was less than $160 per case, including culture plates and laboratory staff time.

Conclusion:
While NAAT testing has high sensitivity and specificity for both GC and chlamydia, 7% of those who were positive for GC would have been missed if only cervical testing had been done. While the overall positivity rate for GC rectal cultures was just under 1%, the added cost per case identified is low compared to the cost of cases identified through NAAT testing (greater than $300 per case).

Implications:
Implementing rectal GC testing is a low-cost way to identify gonorrhea cases missed by cervical NAATs.