Taj Jadavji

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.

OBJECTIVESnTo 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 Childrens Hospital and current practices in other Canadian hospitals. A secondary objective was to characterize features that may predict NAD or CAD etiology.nnnSTUDY DESIGNnRetrospective cohort study and telephone survey.nnnSETTINGnAlberta Childrens Hospital (retrospective review) and Canadian tertiary care paediatric centres (telephone survey).nnnMETHODSnThe 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.nnnRESULTSnFour 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.nnnCONCLUSIONSnThere is a need for the re-evaluation of routine ova and parasite screening, and bacterial culture in nonoutbreak episodes of NAD in children.

HIV infection after prenatal screening: an open window leading to perinatal infection

ABSTRACT Despite a dramatic decrease in vertical transmission of HIV in the developed world, maternal HIV infection acquired after negative prenatal screening still leaves a window of vulnerability. Through quality assurance programs in two Canadian Provinces, five cases where perinatal HIV transmission occurred despite negative prenatal screening were identified between 2005 and 2015. Maternal risk factors such as intravenous drug use, high–risk sexual behavior, hepatitis C virus co–infection, and belonging to high prevalence minority groups were common. Two mothers had their negative HIV test performed in the first trimester and three mothers had negative testing in the third trimester. All babies were clinically healthy at delivery with a normal weight. Three babies were tested following subsequent identification of maternal HIV infection and two babies presented with opportunistic infections leading to their diagnoses. The characteristics of these cases suggest that to achieve complete elimination of vertical HIV transmission, selective and innovative clinical management of mothers at high risk for HIV may be required.