Evaluation of the Strep A OIA assay versus culture methods: ability to detect different quantities of group A Streptococcus.

The Strep A OIA assay by Biostar (Boulder, Co., USA) is a unique optical immunoassay system for the rapid detection of Group A streptococcal carbohydrate. As part of a community-based pediatric cohort study of Group A Streptococcus (GAS) persistence following antibiotic therapy of pharyngitis, the performance of the Strep A OIA assay was compared with the amount of growth from standard throat swab culture methods. A total of 363 throat swabs taken over the course of the study was evaluated from 248 children between 2 and 18 years of age. Two culture methods were performed: an agar plate with the throat swab using Columbia agar base with 5% sheep blood incubated under an anaerobic environment for 48 h and Todd-Hewitt broth (THB) enhancement. The Strep A OIA was then performed. A total of 144 of 363 (39.7%) samples was positive for GAS by one or more of the laboratory tests across study visits: agar culture detected 132 of 144 (91.7%), THB culture detected 128 of 144 (88.9%), and the Strep A OIA assay detected 129 of 144 (89.6%). Complete agreement among all three laboratory tests was found for 333 of 363 (91.7%) of the samples. Agar culture results were comparable to THB cultures with a sensitivity of 96.9%, specificity of 96.6%, a positive predictive value of 93.9%, and a negative predictive value of 98.3%. Although the performance of the Strep A OIA assay had similar specificity (96.5%) and positive predictive value (93.8%) compared with the combined results of the two culture methods, the sensitivity (89.0%) and negative predictive value (93.6%) were lower. A significant difference (p < 0.001) was found in the ability of the Strep A OIA assay to detect agar culture-positive swabs that had a light growth (1+ or 2+) (63.0%) versus a moderate (3+) or heavy (4+) growth (98.1%) of GAS. Although the Strep A OIA assay allows GAS throat swab results to be reported an average of 24 h sooner than either of the cultures, the rapid assay was not as sensitive in detecting light growth GAS-positive cultures.

Differential yield of pathogens from stool testing of nosocomial versus community-acquired paediatric diarrhea.

OBJECTIVES: To evaluate the role of routine stool examination for all pathogens in paediatric nosocomial diarrhea (NAD) and community-acquired diarrhea (CAD) over a two-year period at Alberta Children's Hospital and current practices in other Canadian hospitals. A secondary objective was to characterize features that may predict NAD or CAD etiology. STUDY DESIGN: Retrospective cohort study and telephone survey. SETTING: Alberta Children's Hospital (retrospective review) and Canadian tertiary care paediatric centres (telephone survey). METHODS: The health and microbiological records of all children with an admission or discharge diagnosis of diarrhea were reviewed using a standardized data collection form. In addition, a telephone survey of laboratories serving all paediatric hospitals in Canada was conducted using a standard questionnaire to obtain information about practices for screening for pathogens related to NAD. RESULTS: Four hundred and thirty-four CAD episodes and 89 NAD episodes were identified. Overall, rotavirus and Clostridium difficile were the most commonly identified pathogens. Bacterial culture was positive in 10.6% CAD episodes tested, with Escherichia coli O157:H7 identified as the most common non-C difficile organism. In NAD, no bacteria were identified other than C difficile (toxin). Screening for ova and parasites had negligible yield. Viruses were more frequent in the winter months, while bacterial pathogens were more common in the summer and fall months. Over 50% of Canadian paediatric hospitals still routinely process NAD specimens similarly to CAD specimens. CONCLUSIONS: There is a need for the re-evaluation of routine ova and parasite screening, and bacterial culture in nonoutbreak episodes of NAD in children.

Predictors and outcome of admission for invasive Streptococcus pneumoniae infections at a Canadian children's hospital.

Rates of admission for invasive Streptococcus pneumoniae infection in children vary considerably between institutions. We performed a retrospective study to investigate factors used in the decision to admit patients with invasive S. pneumoniae infection to Alberta Children's Hospital. Of 254 patients who were initially assessed in the emergency department, 38.2% were admitted to the hospital. Significant risk factors for admission as determined by a logistic regression model included murmur (odds ratio [OR], 18.98; 95% confidence interval [CI], 4.08-88.23), focal infection (OR, 11.41; 95% CI, 5.07-25.67), and older age (OR, 2.72; 95% CI, 1.03-7.17). Higher hemoglobin level (OR, 0.96; 95% CI, 0.93-0.99) and temperature of > 38.5 degrees C (OR, 0.39; 95% CI, 0.18-0.85) were associated with a lower risk of admission. Two patients died (case-fatality rate, 0.7%). Despite the low rate of admission for invasive S. pneumoniae infections at our hospital, the mortality rate was comparable with those at institutions with higher rates of admission, thus suggesting that the factors we identified may be useful in deciding whether to admit patients with (or who are at high risk for) invasive S. pneumoniae infections.

Extended incubation of culture plates improves recovery of Bordetella spp.

Extended incubation of culture plates was studied to see if the recovery of Bordetella spp. from nasopharyngeal swabs could be improved. Forty-eight Bordetella isolates were recovered from 103 children (overall positive-culture rate, 46.6%) who met the clinical case definition of pertussis. Seven of 44 (16%) B. pertussis isolates and 2 of 4 (50%) B. parapertussis isolates were recovered only after extended incubation of nasopharyngeal cultures up to 12 days.