BACKGROUND: Kansas regulations exclude persons with Shiga toxin-producing Escherichia coli (STEC) infection from delivering health care, handling food, and providing or attending daycare until 2 consecutive negative convalescent stool culture results are obtained. Increasingly, laboratories use multiplex polymerase chain reaction (PCR) panels to detect presence of STEC instead of classic biochemical culture methods. Use of PCR to confirm absence of STEC in convalescent specimens has not been assessed. We compared culture with PCR for testing convalescent specimens to determine the potential effect of PCR use on persons excluded from work or daycare (“excluded persons”).
METHODS: Required convalescent stool specimens collected ≥48 hours after symptom resolution from excluded persons (previously diagnosed by any method) and submitted during August–November 2016 were evaluated. Specimens were tested for STEC using classic biochemical culture and PCR. Specimens from excluded persons were collected and tested until 2 consecutive negative cultures were obtained and the exclusion was lifted.
RESULTS: Seven excluded persons submitted 26 specimens; 46% (12/26) were culture and PCR positive; 19% (5/26) were culture and PCR negative; and 35% (9/26) were culture negative and PCR positive. Among each person’s last 2 culture-negative specimens, PCR test results were both negative (n=2), positive followed by negative (n=1), and both positive (n=4).
CONCLUSIONS: PCR detected Shiga toxin nucleic acid targets in a majority of culture-negative convalescent specimens. If PCR was used instead of culture, 5 of 7 exclusions would not have been lifted. PCR can detect Shiga toxin nucleic acid in non-viable bacteria, thus culture remains the preferred method for STEC testing on convalescent specimens in Kansas. As laboratory capacity for PCR increases further evaluation of PCR use for convalescent testing is warranted.