An evaluation of repeat stool testing for Clostridium difficile infection by polymerase chain reaction.

Goals: To evaluate the yield of repeat stool polymerase chain reaction (PCR) testing in patients with suspected Clostridium difficile infection (CDI).
Background: CDI is a major challenge in health care due to its frequent occurrence and high associated costs. Enzyme immunoassay and PCR are commonly performed diagnostic tests for CDI.
Methods: Our microbiology laboratory database was queried from January 1, 2008 to June 30, 2010 for all patients who underwent PCR stool testing for suspected CDI. Data collected included age, sex, number of stool tests performed within a 14-day period after the first test, and location of patient (inpatient vs. outpatient). Analyses were performed using JMP version 9.0.1.
Results: PCR testing was performed in 15,515 patients. The median age was 58.3 years (range, 10 d to 104.3 y) and 46.2% of patients were women. Repeat testing was infrequent; 87.3% of patients had testing performed only once in a 14-day period. Increased age, male sex, and inpatient location were predictors of repeat testing. The median time between an initial test and the first repeat test was 5 days. After an initial negative test, the percentage of patients having a subsequent positive test was low (2.7% in 7 d and 3.2% in 14 d). The percentage of repeat tests that was positive within 7 days (2.9%) was lower than the percentage that was positive from day 8 to day 14 (4.8%, P=0.05).
Conclusions: Repeat testing for C. difficile has a low yield, and patients with an initial negative test should not routinely be retested.