Risk factors for Clostridium difficile stool cytotoxin b among critically ill patients: role of sucralfate.

To identify risk factors other than antimicrobial exposure for Clostridium difficile stool cytotoxin b, subjects admitted to critical care units over 18 months and who had stool cytotoxin assays were evaluated. Twenty-two cases (cytotoxin b-positive) were compared with 125 controls (cytotoxin b-negative). Cases and controls were similar with respect to age, sex, therapeutic index severity score, duration of hospitalization before cytotoxin b testing, and antimicrobial exposure. Adjusted odds ratios (OR) revealed white blood cell count of > 12,000 on the day of stool sampling (OR, 4.0; 95% confidence interval [CI], 1.3-12.4) and sucralfate exposure (OR, 0.15; 95% CI, 0.05-0.42) as significant independent positive and negative risk factors, respectively. Sucralfate exposure may decrease risk for C. difficile stool cytotoxin b by interfering with its detection, altering toxin production, or inhibiting colonization by the organism. Additional evaluation is needed to elucidate the mechanisms involved.

Comparison of direct specimen testing utilizing TestPack strep A with testing of specimens following a two-hour broth enrichment.

In a previous study, we demonstrated that a 2-h enrichment of throat swabs in broth followed by a direct fluorescent antibody test was significantly more sensitive than the Abbott TestPack Strep A for the detection of group-A streptococci. In this study, in an effort to simplify the technique, we utilized broth enrichment with an enzyme immunoassay detection method. A total of 1017 pharyngeal specimens were tested with TestPack Strep A (DTP), culture on a selective streptococcal agar, and a 2-h broth enrichment in Todd-Hewitt broth (THB) followed by TestPack Strep A (ETP). Subculture of the THB was used to arbitrate discordant test results. The sensitivities and specificities respectively were as follows: DTP (69% and 99%), ETP (90% and 98%), and SSA (97% and 100%). This enrichment method offers significantly greater sensitivity than direct testing for antigen yet still allows the potential for finalized same-day reporting of results.

Comparison of three methods for detection of group A streptococci in throat swabs.

Group A streptococci are generally detected in throat swabs by (i) rapid antigen tests, (ii) conventional culture, or (iii) combinations of both. Direct fluorescent-antibody testing of a 2-h enrichment broth (FA/EN) was an accepted method for same-day results before the advent of rapid antigen tests. We compared FA/EN in Todd-Hewitt Broth (THB) with conventional culture and a rapid antigen test, TestPack Strep A (TPS). Nine hundred seventy specimens were evaluated in this study. Cultures were performed for 48 h on sheep blood agar (SBA) incubated aerobically and on a selective agar for group A streptococci (SSA) incubated in 5 to 10% CO2. Following a 2-h incubation, the fluorescent-antibody test was performed. A subculture of the centrifuged sediment from the THB enrichment was also done. In comparison with a positive culture on SBA or SSA or subculture of the THB pellet, the sensitivities and specificities of the different methods were as follows: SBA, 92 and 100%; SSA, 92 and 100%; TPS, 68 and 99%; FA/EN, 88 and 98%. The FA/EN method offers the potential for definitive finalized reports on the same day as specimen collection with greater sensitivity than TPS. This study included sequential plating and rapid antigen testing of a single swab. In a separate set of experiments to validate this study design, it was shown that recovery of streptococci from swabs plated sequentially on five plates did not vary with the order of plating and the actual proportion of organisms recovered from a swab on a single plate was only 1%.

Nonvalue of terminal aerobic subculture of unvented Roche Columbia broth blood culture bottles.

This study evaluated the need for a terminal aerobic blind subculture of unvented Roche Columbia broth. Only 2 of 2,871 bottles subcultured grew clinically significant organisms that were not also found in another blood culture. We conclude that in our tertiary care institution, blind subcultures of Roche Columbia broths are unwarranted.