Rapid testing methods in microbiology

Sept. 1, 2011
This photograph (circa 1963) from the CDC depicts a laboratorian performing an examination of an agar culture Petri dish, which had been inoculated with Salmonella typhi. Modern day protocols call for laboratorians executing such tasks to wear personal protective equipment (e.g., safety goggles, gloves, and a face mask).

Reduce diagnostic guesswork — expand your STAT menu

Having worked a number of 13-week temporary microbiology assignments in various parts of the U.S., I have seen firsthand a huge diversity in laboratory practices — some not so good. In my previous diary entries here, I noted this as a symptom of poor, inconsistent, and “clueless” administrative decision making. Misguided cost issues, pressure not to increase workload, and just plain inertia are all to blame for the snail’s pace to change. More and more real-time testing methods are available to help reduce the guesswork associated with emergency medicine, to jump-start appropriate therapy, and reduce hospital inpatient stays.

Diarrheal illness

Cryptosporidium and Giardia antigens assays can be performed on stool samples within an hour of receipt of the specimen in the lab if these tests are available on the STAT menu and also can alert epidemiologists of a potential outbreak.
  • Rotavirus antigen test — Proper diagnosis of etiologic agents of diarrhea can guide appropriate therapy, most often supportive. Rotavirus is no longer only a dehydrating winter diarrhea in infants and small children. Group B rotavirus primarily causes cholera-like diarrhea in adults and is slowly making its way to the U.S. from China, Hong Kong, United Kingdom, and Australia.
  • Shiga-toxin assays should replace specific culture for enterohemorrhagic Escherichia coli (EHEC) 0157:H7 since close to 50% of EHEC are non-0157:H7 serotypes. Because antimicrobial therapy may have disastrous consequences, early detection of this causative agent is tantamount.
  • Norovirus antigen test (winter vomiting disease) — Early detection of an outbreak can help to reduce the spread of infection.
  • Campylobacter antigen tests — antimicrobial therapy can shorten the course of disease, if detected early.
  • Clostridium difficile toxin A/B — Rapid methodologies for the detection of these toxins are crucial on many levels, but recent studies are reporting they are less sensitive and specific than was previously believed.
  • The Gram stain can be a powerful diagnostic tool for the differential diagnosis of diarrheal illness. The presence or absence of inflammatory cells (white blood cells or WBCs) can help to narrow down the causes of diarrhea. Bacteria causing diarrhea usually produce abundant WBCs in the stool specimen whereas viral or parasitic infections do not.
  • Community-acquired pneumonia (CAP):

    • Streptococcus pneumoniae and Legionella urinary antigen — This test provides an immediate, simple, rapid method for the diagnosis of infection that is conveniently collected and transported.
    • Mycoplasma pneumonia IgM STAT — Mycoplasma pneumonia is the most common etiological agent of lower respiratory-tract infection in patients younger then 30 years old. Cultures for this organism make take as long as five days, so rapid methodologies targeting the acute-phase antibody makes sense.
    • The Gram stain can be a valuable tool for the diagnosis of bacterial pneumonias. Screening for sputum acceptability and stringent technologist proficiency in microscopy is tantamount to accuracy in reporting.

    Immediately available diagnostic-testing tools can mean quicker recovery rates and less usage of the “BMW” of expensive broad-spectrum “shot-gun” antimicrobials — or can alert the provider that administration of any antibiotic can have tragic consequences.

    —By Colleen K. Gannon, MT(AMT) HEW, Un-retired,
    the “Nancy Grace” for labs