Testing for biological agents
Quick diagnosis and treatment of a patient exposed to a biological agent are key to saving that patient's life. A biological attack may go unnoticed until large groups of people begin exhibiting symptoms, which makes prompt diagnosis even more critical. But getting a quick medical answer is complicated by the fact that currently there is no single test that can diagnose whether a person has been exposed to biological agents. There are clinical trials underway, however, on better testing methods.
To look for evidence of biological agents, physicians will take blood or other samples to be tested at clinical laboratories. As the clock is ticking, the sample must be collected and sent to the appropriate lab for analysis. However, it takes time to isolate the bacteria, toxin, or virus from the sample. This time frame can stretch from hours to days, depending on the agent, the amount of exposure, the proximity and capabilities of the lab, and the time the test(s) take. The following list provides descriptions of the types of tests that may be run:
Environmental testing is examining a building or an area for the presence of a biological or chemical agent. Testing is usually a two-step process. Using anthrax as an example, if the sample contains a large amount of the bacteria (Bacillus anthracis), a positive reading may come back within minutes. However, this quick initial result from the scene may be what is called a false positive result, so a more reliable test must be done by a more sophisticated laboratory to confirm the results. The confirmation test can take up to 72 hours depending on how fast the bacteria grow and can be positively identified.
A nasal swab is an environmental test that may be used to assist in a public-health investigation to determine the presence of a bioterrorism agent in an area or building. Nasal swabs are not used to determine if a person is infected by a given agent.
A culture is a method for growing an organism in the lab (for example, in a petri dish). A culture can help in identifying a bacteria or virus. Cultures are the most readily available technology for clinical diagnosis of a suspected case of bioterrorism but can be time consuming to complete.
A blood culture is a test that looks for bacteria or viruses in the blood. Blood is drawn from a patient, and the sample is sent to a special laboratory for analysis. The sample is incubated, or kept in a warm place, at a certain temperature, and in this controlled environment, the bacteria grow and are isolated from the blood for easier identification.
"Media" are the nutrient mixes used to grow organisms in a lab. Selective media are used to identify an organism by giving it or depriving it of certain nutrients. For example, selective agents can be added or removed, which "poison" some organisms while allowing others to grow.
Gram staining uses dyes to make a bacterial cell stand out for identification. A specimen is put on a slide, and a four-part staining procedure begins. This test may produce results in less than an hour, but it is not specific enough to definitely identify the organism, and a longer confirmation test is still needed.