[External quality controls for allergy analysis in the Quality Control Center Switzerland from 2006 to 2008]. / Les contrôles de qualité externes pour le laboratoire d'allergologie auprès du Centre suisse de contrôle de qualité de 2006 à 2008.

External assessment of analytical performance is part of the quality assurance in medical laboratory. These external controls are mandatory in Switzerland since 2006 for IgE analysis. The Swiss Society for Immunology and Allergy and the Swiss external quality centers had launched a program for total IgE, IgE specific for cat epithelium, birch pollen and peanut, and multi-specific IgE. They have set up criteria for proficiency assessment. Analysis of data obtained from 2006 to 2008 in the Quality Control Center Switzerland shows that results are very good for all the methods used and that a large number of participants fulfill the requirements to obtain the certificate of QUALAB conformity.

[Performances of rapid antigen detection kits for group A Streptococcus]. / Performances des trousses de dépistage rapide des streptocoques du groupe A.

The group A streptococcus rapid antigen detection kits used to test throat swabs are frequently used by doctors for the screening of pharyngitis caused by bacteria. The Swiss Centre for Quality Control (CSCQ) has organised External Quality Assessment Schemes (EQAS) for these kits since 1997. From 2004 to 2008, negative, positive, and moderate positive antigen containing samples were sent to the laboratories. After analysing the samples, 7749 results obtained with more than 14 different test kits were returned to the CSCQ. The correct results ranged between 84.8 and 99.8% which shows that all the test kits gave good results during the EQAS. However, in case of a negative result with clinical suspicion of a bacterial pharyngitis, the result is to be confirmed by culture.

External quality control of direct antigen tests to detect group A streptococcal antigen.

Presented here are the results of an external quality control survey organized by the Swiss Center for Quality Control (CSCQ) to evaluate the performance of direct antigen tests (DATs) widely used in Swiss medical practices and laboratories for the diagnosis of group A streptococcal pharyngitis. Twice yearly over a 4-year period, just over 100 participants were requested to analyze positive, weakly positive and negative samples provided to them by the CSCQ with their routinely used DATs and to send the results to the CSCQ. For 1,620 samples distributed, the CSCQ received 1,484 (91.6%) results obtained with 17 different DATs. The specificity of all DATs for negative samples was >91%. For samples containing abundant group A streptococcal antigen, sensitivities ranged from 59.1% to 95.5%; however, for samples containing low levels of antigen, the sensitivity was much lower for all DATs, ranging from 8.7% to 69.8%. Therefore, negative DAT results should be verified with well-performed cultures in order to assure the optimal care of patients with pharyngitis.

Detection of enteroviruses in the cerebrospinal fluid by polymerase chain reaction: prospective study of impact on the management of hospitalized children.

A polymerase chain reaction kit (AMPLICOR EV) for the detection of enteroviruses (EV-PCR) in the cerebrospinal fluid (CSF) was evaluated in clinical conditions in a prospective blinded-intention study. Forty-three children (mean age 2.7 years) hospitalized for suspected meningitis or fever of unclear etiology were enrolled. EV-PCR was performed on a daily basis. Results were available in less than 2 days in 72% of cases. EV-PCR was positive in nine (21%) children, including three infants without CSF pleocytosis. Knowing their EV-PCR result would have allowed a saving of 18 hospital days and 12 days of antibiotic therapy. The EV-PCR in the CSF can thus be practically useful for children hospitalized for meningitis or fever if available on-site on a daily basis.

Detection of human immunodeficiency virus type 1 (HIV-1) RNA in pools of sera negative for antibodies to HIV-1 and HIV-2.

A total of 234 pools were prepared from 10,692 consecutive serum samples negative for antibodies to human immunodeficiency virus type 1 (HIV-1) and HIV-2 collected at five virological laboratories (average pool size, 45 serum samples). Pools were screened for the presence of HIV-1 RNA by a modified commercial assay (Amplicor HIV-1 Monitor test) which included an additional polyethylene glycol (PEG) precipitation step prior to purification of viral RNA (PEG Amplicor assay). The sensitivity of this assay for HIV-1 RNA detection in individual serum samples within pools matches that of standard commercial assays for individual serum samples, i.e., 500 HIV-1 RNA copies per ml. Five pools were identified as positive, and each one contained one antibody-negative, HIV-1 RNA-positive serum sample, corresponding to an average of 1 infected sample per 2,138 serum samples. Retrospective analysis revealed that the five HIV-1 RNA-positive specimens originated from individuals who had symptomatic primary HIV-1 infection at the time of sample collection and who were also positive for p24 antigenemia. We next assessed the possibility of performing the prepurification step by high-speed centrifugation (50,000 x g for 80 min) of 1.5-ml pools containing 25 microl of 60 individual serum samples, of which only 1 contained HIV-1 RNA (centrifugation Amplicor assay). The sensitivity of this assay also matches the sensitivities of standard commercial assays for HIV-1 RNA detection in individual serum samples. The results demonstrate that both assays with pooled sera can be applied to the screening of large numbers of serum samples in a time- and cost-efficient manner.