THE JOHNS HOPKINS MICROBIOLOGY NEWSLETTER Vol. 24, No. 16
Tuesday, May 3, 2005
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Provided by Sharon Wallace, Division of Outbreak Investigation, Maryland Department of Health and Mental Hygiene.
4 outbreaks were reported to DHMH during MMWR Week 17(April 24 - April 30):
2 Gastroenteritis Outbreaks
1 outbreak of GASTROENTERITIS associated with a Nursing Center in Montgomery Co.
1 outbreak of FOODBORNE GASTROENTERITIS associated with a Nursing Center in Calvert Co.
2 Respiratory Outbreaks
1 outbreak of PNEUMONIA associated with a Nursing and Rehabilitation Center in Prince Georges Co.
1 outbreak of INFLUENZA-LIKE ILLNESS/PNEUMONIA associated with a Nursing Center in Montgomery Co.
The Johns Hopkins Hospital, Department of Pathology, Information provided by, Kathleen Burns, M.D., Ph. D
The Respiratory Viral Season
Technicians in the virology laboratory are breathing a little easier as respiratory viral season 2004-2005 is waning. This newsletter describes briefly
how the laboratory diagnosis of influenza and respiratory syncytial virus (RSV) is made, as well as provides the tallies of our cases this year.
Each of us may have on average two to four viral upper respiratory infections a year, and children can easily average twice as many. Lower
respiratory tract involvement is fortunately less common, though still poses danger to many young, old, and immunocompromised each year. Some of
the most common important pathogens diagnosed, particularly this time of year, are influenza A and B and RSV viruses. Other viral infections are also
associated.
Diagnostic Testing
Laboratory diagnosis hinges on rapid testing by enzyme immunoassay (EIA), direct immunofluorescent assays (DFAs) to detect viral antigens in
specimens, and tissue culture, both standard and rapid/RMIX shell vial methods. We are using with Binax EIA for rapid testing, and do not go on to do
DFA and culture in positive specimens during the season. Culture, however, remains the gold standard in terns of sensitivity and is done on all EIA
negative specimens. While it is being replaced by alternative testing methods at many places, culture enhances viral detection and will remain a critical
method for analyzing changes in viral antigens for purposes of epidemiologic studies and vaccination efforts.
Appropriate specimens for rapid testing include nasopharygeal aspirates and washes; appropriate specimens for DFA and cultures also include
bronchoalveolar lavages and endotrachael aspirates.
Case Tallies for the 2004-2005 Season at Hopkins
Of the more than 3500 respiratory antigen and culture orders placed between October and April, 726 (approximately 20%) were identified as positive
by Binax rapid testing for influenza A (392), influenza B (184), or RSV (150). The other specimens were tested by DFA and cultured to give the
following totals.
Using EIA, DFA and culture, there was a total 635 influenza A cases, 482 influenza B cases, and 275 RSV cases. Other viruses were found more
rarely, the greatest numbers being 56 for CMV and 59 for HSV. For Influenza A, 61% were identifiable on EIA, 17% more were appreciable on DFA,
and 22% of positive results depended on culture. For influenza B, EIA identified 38%, DFA an additional 5%, and culture 57%. For RSV, EIA
identified 55%, DFA 32%, and culture 13%.
The shell vial culture method was employed in parallel with traditional culture; in shell vials inoculated viruses are centrifuged
against a cell monolayer grown on a coverslip. The cells are stained with fluorescent monoclonal antibodies after a relatively short
incubation period before cytopathic effect may be appreciated in traditional culture. Although laborious, it may allow earlier
reporting of positive results. The method had an overall sensitivity in our hands of about 70% as compared to culture, and was
99%+ specific.
Special Acknowledgment
My thanks to Mrs. Debbie Aird for teaching me this methodology and providing these interesting data, during a very busy time!