How is anthrax diagnosed? Anthrax Laboratory Testing

by CDC

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How is anthrax diagnosed?

Anthrax is diagnosed by isolating B. anthracis from the blood, skin lesions, or respiratory secretions or by measuring specific antibodies in the blood of persons with suspected cases.

In patients with symptoms compatible with anthrax, providers should confirm the diagnosis by obtaining the appropriate laboratory specimens based on the clinical form of anthrax that is suspected (i.e., cutaneous, inhalation, or gastrointestinal).

What are the standard diagnostic tests used by the laboratories?

Presumptive identification to identify to genus level (Bacillus family of organisms) requires Gram stain and colony identification.

Presumptive identification to identify to species level (B. anthracis) requires tests for motility, lysis by gamma phage, capsule production and visualization, hemolysis, wet mount and malachite green staining for spores.

Confirmatory identification of B. anthracis carried out by CDC may include phage lysis, capsular staining, and direct fluorescent antibody (DFA) testing on capsule antigen and cell wall polysaccharide.

When is a nasal swab indicated?

Nasal swabs and screening may assist in epidemiologic investigations, but should not be relied upon as a guide for prophylaxis or treatment. Epidemiologic investigation in response to threats of exposure to B. anthracis may employ nasal swabs of potentially exposed persons as an adjunct to environmental sampling to determine the extent of exposure.

Is there an X-ray for detecting anthrax?

A chest X-ray can be used to help diagnose inhalation anthrax in people who have symptoms. It is not useful as a test for determining anthrax exposure or for people with no symptoms.

Can someone get anthrax from contaminated mail, equipment or clothing?

In the mail handling processing sites, B. anthracis spores may be aerosolized during the operation and maintenance of high-speed, mail sorting machines potentially exposing workers. In addition, these spores could get into heating, ventilating, or air conditioning (HVAC) systems. CDC interim guidelines have been issued to advise workers on how best to protect themselves in the workplace.

Anthrax Laboratory Testing

Can I get screened or tested to find out whether I have been exposed to anthrax?

There is no screening test for anthrax; there is no test that a doctor can do for you that says you've been exposed to or carry it. The only way exposure can be determined is through a public health investigation. Nasal swabs and environmental tests, are not tests to determine whether an individual should be treated. These kinds of tests are used only to determine the extent of exposure in a given building or workplace.

If patients are suspected of being exposed to anthrax, should they be quarantined or should other family members be tested?

Anthrax is not known to spread from one person to another person. Therefore, there is no need to quarantine individuals suspected of being exposed to anthrax or to immunize or treat contacts of persons ill with anthrax, such as household contacts, friends, or coworkers, unless they also were also exposed to the same source of infection.

Does CDC collect samples to test the bacteria?

CDC is engaging its partners in the Laboratory Response Network (LRN) in states all across the United States. The LRN is a collaborative partnership and multilevel system linking state and local public health laboratories with advanced capacity laboratories - including clinical, military, veterinary, agricultural, water, and food-testing laboratories - to rapidly identify threat agents, including anthrax. Local clinical laboratory testing is confirmed at state and large metropolitan public health laboratories. CDC conducts the definitive or highly specialized testing for major threat agents. There are 100 laboratories in the network; none of them are commercial labs.

When an area is tested for the presence of Bacillus anthracis, how long does it take to get the results?

Before testing can begin, samples must be collected in a form suitable for testing. The length of time it takes to get test results depends on both the kind of test to be performed and the laboratory's workload. Some tests may take only a short time to perform, but confirmation takes longer. It may take many days to get the test results.

Testing is a two-step process. The first test, a screening test, may be positive within 2 hours if the sample is large and contains a lot of Bacillus anthracis, the organism that causes the disease anthrax. However, a positive reading on this first test must be confirmed with a second, more accurate test. This confirmation test, conducted by a more sophisticated laboratory, takes much longer. The length of time needed depends in part on how fast the bacteria grow, but results are usually available 1 to 3 days after the sample is received in the laboratory.

Does CDC recommend the use of home test kits for anthrax?

Hand-held assays (sometimes referred to as "Smart Tickets") are sold commercially for the rapid detection of Bacillus anthracis. These assays are intended only for the screening of environmental samples. First responder and law enforcement communities are using these as instant screening devices and should forward any positive samples to authorities for more sensitive and specialized confirmatory testing. The results of these assays should not be used to make decisions about patient management or prophylaxis. The utility and validity of these assays are unknown.

At this time, CDC does not have enough scientific data to recommend the use of these assays. The analytical sensitivity of these assays is limited by the technology, and data provided by manufacturers indicate that a minimum of 10,000 spores is required to generate a positive signal. This number of spores would suggest a heavy contamination of the area (sample). Therefore a negative result does not rule out a lower level of contamination. Data collected from field use also indicate specificity problems with some of these assays. Some positive results have been obtained with spores of the non-anthrax Bacillus bacteria that may be found in the environment.

For these reasons, CDC has been asked to evaluate the sensitivity and specificity of the commercially available, rapid, hand-held assays for B. anthracis. When this study is completed, results will be made available. Conclusions from this study are not expected in the near future.

About the Author

www.cdc.gov
The Centers for Disease Control and Prevention (CDC) is one of the 13 major operating components of the Department of Health and Human Services (HHS), which is the principal agency in the United States government for protecting the health and safety of all Americans and for providing essential human services, especially for those people who are least able to help themselves.