Susan Richardson, MD FRCPC

Biography

Susan Richardson, MD FRCPC

Dr. Susan Richardson is a medical microbiologist and infectious diseases physician. Dr. Richardson obtained her MD from McGill University and has fellowships in Internal Medicine, Infectious Diseases and Medical Microbiology from the Royal College of Physicians and Surgeons of Canada. She is an Associate Scientist in the Research Institute at The Hospital for Sick Children and Associate Professor in the Department of Pathobiology and Laboratory Medicine at the University of Toronto. Dr. Richardson was appointed Head of the Division of Microbiology at The Hospital for Sick Children in July 2002, and Consultant in Mycology to the Central Public Health Laboratory, Toronto in 2005. Her research interests are in the areas of mycology, where she is actively engaged in studies on fungal infections in immunocompromised patients, and in the area of the rapid diagnosis of viral respiratory infections, especially SARS-CoV and influenza. Dr. Richardson served as President of the Association of Medical Microbiology and Infectious Disease Canada (AMMI Canada) from 2004-2006 and is now serving a two year term as Past-President.

Introduction of a New Program to Lower Sample Rejection Rates and Improve Rapid Direct Detection of Respiratory Viruses in Children.

Background

Prior to the 2002-3 respiratory season, the rejection rate for DFA on polyester nasopharyngeal swabs (NPS) for respiratory virus detection in children in our institution was 11- 15% per year. Based on a study showing equivalence of NPS and nasal swabs (NS) for the detection of respiratory viruses in children in an outpatient setting, and following staff education, NS became the recommended specimen type. Soon after institution of NS sampling, DFA rejection rate rose to 22-27% per year, with rates as high as 38% on some wards. High rates of rejection of NS were unaffected by repeated in-service education efforts to improve the yield by addressing technical aspects of obtaining these specimens.

Objective

To study the effect of swab type (polyester vs. flocked) and specimen type (NS vs. NPS) on yield of respiratory viruses by direct fluorescent antibody (DFA) testing and viral isolation.

Methods

A pilot study (n=121) of flocked swabs (Copan) vs. polyester swabs (Puritan) for detection of respiratory viruses from NS of children with suspected viral infection was performed 11/05-01/06 on 3 wards with the highest rate of rejection of specimens for DFA due to insufficient cellular sampling. This was followed by a repeat study (n=146) on the same wards (09/06-02/07), using the same two swab types, but sampling the nasopharynx. Quantitation of cells by swab type (insuff, 1+, 2+, 3+, 4+), DFA rejection rates, DFA positivity rates and yield of viral isolation was compared between the two groups. Each child was tested with both swab types, one per nare, in each study. All specimens were tested by DFA/culture for influenza A/B, parainfluenza 1,2,3, adenovirus, RSV and human metapneumovirus.

Results

The 2005/6 pilot study of flocked vs. polyester NS showed rejection rates of 32.8% (42/128) and 22.3% (27/121), respectively. The 06/07 study of flocked vs. polyester NPS revealed a dramatically reduced rejection rate of 11.0% (16/146) for flocked swabs vs. 28.1% (41/146) for polyester. For those specimens with adequate cells for analysis, 60% had 3-4+ cells using flocked swabs vs. 43% for polyester swabs. 32 NPS were DFA positive by both flocked and polyester swabs, 3 by flocked only and 2 by polyester only. 5/112 (4.5%) were culture pos/DFA neg, all RSV with =2+ cells. 8/144 (5.6%) were culture neg/DFA pos, 5 RSV, one each of influenza A, parainfluenza 1, 3.

Conclusions

In our cohort of children presenting/admitted to hospital, two factors appear to be necessary for optimal sampling of the upper airway for respiratory virus detection: nasopharyngeal sampling rather than nasal, and the use of flocked swabs rather than polyester swabs. Staff education and re-education is also critical, but was not as important as swab type or sampling site.