Polymerase chain reaction for Streptococcus pyogenes used to evaluate an optical immunoassay for the detection of group A streptococci in children with pharyngitis

BACKGROUND.In evaluations of sensitive rapid tests for group A streptococci such as the optical immunoassay (OIA), some samples are positive by the antigen test but negative by culture. A method is needed for resolving these discrepant results. OBJECTIVE.To develop a PCR-based assay to detect group A streptococci and to use it to establish a reference standard for evaluating an OIA for group A streptococcal antigen. METHODS.A PCR assay that detects a segment of the MF gene of Streptococcus pyogenes was developed for the detection of group A streptococci in throat swabs. Paired swabs were obtained from 200 children with symptomatic pharyngitis and used to perform OIA, agar culture, brothenhanced culture and PCR. As a reference standard any patient with group A streptococci detected by either culture or PCR was considered to be truly positive. RESULTS.In comparison to agar and broth-enhanced culture procedures, OIA had sensitivities of 82 and 80% and specificities of 87 and 89%, respectively. Eight (44%) of 18 samples that were positive by OIA but negative by culture were positive for group A streptococci by PCR. Compared with the reference standard, sensitivities were OIA 76%, agar culture 79%, broth-enhanced culture 86% and PCR 96%. The specificity of OIA was 92%. CONCLUSIONS.PCR can be used to establish a reference standard for evaluating rapid tests for group A streptococci. With this reference standard OIA was nearly as sensitive as but less specific than agar culture for detection of group A streptococci. Maximum detection requires use of both tests

Contaminated Ventilator Air Flow Sensor Linked to Bacillus cereus Colonization

We investigated Bacillus cereus–positive tracheal aspirates from infants on ventilators in a neonatal intensive care unit. Multilocus sequence typing determined a genetic match between strains isolated from samples from a casepatient and from the air flow sensor in the ventilator. Changing the sterilization method for sensors to steam autoclaving stopped transmission. Because of ubiquity in the environment, the recovery of Bacillus species from clinical specimens is often considered a clinically inconsequential contamination. Nevertheless, an accumulating body of literature suggests that contamination with this organism should not be routinely dismissed (1). Severe and lethal Bacillus cereus infections have been described in newborn infants, with higher frequency among premature infants. The types of B. cereus infections in newborns included central nervous system, respiratory tract, primary bacteremia, and sepsis (2–4). Nosocomial outbreaks of B. cereus implicating hospital linens, manual ventilation balloons, contaminated diapers, and contaminated ventilator equipment have also been reported (5–9). The Study The Missouri Department of Health and Senior Services conducted this investigation in response to the hospital’s identification of an increased number of tracheal aspirates that were positive for B. cereus collected from newborns who were on ventilators during March–May