Some microbes, including bacteria, fungi, parasites and viruses, cause infections in humans. These are known as infectious agents or pathogens. Traditional testing techniques for detection of such pathogens includes, for example, growing microbes in cultures followed by identification of the microbe, or testing blood samples for antibodies that people develop in response to an infection by a particular microbe.
Because microbes contain genetic material, also called nucleic acids (DNA and RNA), that is different from the genetic material in human cells, genetic testing techniques can also be used to detect microbes. Samples that might contain these microbes include urine, blood, sputum, cerebrospinal fluid and stool. In addition to detecting microbes directly in specimens like these, genetic testing techniques may also be used to identify microbes after they have been grown in culture.
Genetic testing may be more sensitive and specific than traditional methods of testing, and provide results faster than other techniques, such as cultures. One particular type of genetic testing is called “NAAT”, which stands for nucleic acid amplification test. This technique makes numerous copies (amplification) of any genetic material from the microbes present in a sample so that it can be more easily detected. One type of NAAT is polymerase chain reaction (PCR).
In addition to identifying the microbes causing an infection, genetic testing may also be used to determine the type (e.g. sub-type, strain or species) of microbe present. This information may help guide treatment of an infection and link multiple cases to a common source of the infection. Some genetic tests identify specific genes that enable a microbe to grow in the presence of an antimicrobial drug or identify a genotype of a virus that will respond to specific treatment. (For additional details, see the section Guiding Treatment below.)
Some newer infectious disease genetic testing techniques can simultaneously test for several different microbes in a single sample to help diagnose the pathogen causing an infection. These are usually referred to as “panels” and are often used for identifying infections that have similar signs and symptoms but can be caused by a wide variety of microbes. For example, you may have symptoms such as stomach pain and diarrhea, which can be caused by a virus (e.g. norovirus), bacteria (e.g. Salmonella) or a parasite (e.g. Giardia). Panels of genetic tests can identify the cause of your infection more quickly, allowing more timely treatment decisions. Some examples of these panels include:
- A panel of molecular genetic tests that can identify the most common viruses or bacteria causing a respiratory infection by testing a sample collected from the back of the nose and throat.
- A panel of molecular genetic tests that can identify the most common bacteria, parasites, or viruses causing infectious diarrhea by testing a single stool sample. (See GI Pathogens Panel).