Gaining popularity in recent years, molecular testing methods have become the infectious disease testing method of choice for many laboratories and healthcare professionals. Molecular infectious disease tests provide highly sensitive and reliable results, can detect infectious pathogens both qualitatively and quantitatively and can produce timely test results enabling better and cheaper patient care.
Sensitive and Reliable Results
Molecular tests tend to be highly sensitive, providing clinicians and patients with more reliable test results than many other testing methods. For example, when using molecular testing for Herpes Simplex Virus (HSV) detection, positive results are detected with more than 95% sensitivity and specificity in most adult cases1. Molecular HSV tests are 75% sensitive and 100% specific for neonatal meningitis1. When using cerebrospinal culture to test for HSV, less than 2% of clinically determined adult HSV encephalitis cases and only 40% of neonatal central nervous system (CNS) disease are detected1. Additionally, molecular tests for HSV provide clinicians with a rapid diagnosis of HSV encephalitis which can prevent brain biopsy and quickly determine the need for acyclovir therapy1. With highly sensitive, reliable and rapid test results, healthcare professionals can feel confident that they are making the right treatment decisions for their patients.
Qualitative and Quantitative Detection
Molecular testing methods allow laboratories and healthcare professionals to detect the presence of pathogens causing infectious disease both qualitatively and quantitatively. Although a qualitative measure of the infectious agent is often sufficient for the detection of many infectious diseases, there are several clinical conditions where the quantification of certain viruses is required to establish, for example, tumor burden or viral load or to monitor a response to therapy.
Quantitative detection of infectious agents can be of particular importance when measuring tumor burden. For example, since the Epstein-Barr virus (EBV) is found within a tumor, clinicians can gather important information concerning the size of a tumor by measuring the amount of EBV present in a patient sample using a quantitative molecular test.2
Of particular importance for immunosuppressed patients, viral load can be established using quantitative molecular tests to identify the amount of certain infectious pathogens such as cytomegalovirus (CMV), Epstein-Barr virus (EBV) and polyoma virus BK (BK Virus). Many people are infected with these viruses and present with a latent, persistent infection with low levels of viral DNA. Unless a patient becomes immunosuppressed, such as after a transplant or due to an immunosuppressive disease, these viruses tend to be clinically insignificant. The virus, however, can be reactivated in an immunosuppressed patient with dire consequences. In immunosuppressed patients, healthcare providers are able to monitor the virus quantitatively using molecular testing to determine when the viral load rises to dangerous levels.2
Quantitative molecular tests can also help to monitor the response to therapy for certain viruses. For example, clinicians can use qualitative molecular tests to initially diagnose HIV, hepatitis C and hepatitis B. Quantitative molecular tests can then be used to monitor a patient's response to therapy by establishing the amount of virus detected in the patient throughout treatment.2
Timely Results
Molecular testing can provide clinicians with infectious disease test results faster than when using other microbiology testing methods. While results may only be obtained in days or even weeks using microbiology methods such as cultures, molecular tests can deliver results in just a few hours. For many infectious diseases, faster test results can enable healthcare professionals to provide better patient care. This can translate to improved patient outcome, reduced hospital stays and reduced cost of antimicrobial saving hospitals and patients both time and money.3
1 Miller, M. Molecular Diagnosis of Infectious Diseases. North Carolina Medical Journal 2007;68(2):115-118.
http://www.ncmedicaljournal.com/mar-apr-07/Miller.pdf
2 Check, W. Viral Virtuoso — RT-PCR as first-line test. CAP Today 2008.
http://www.cap.org/
3 Pfaller, M. Molecular Approaches to Diagnosing and Managing Infectious Diseases: Practicality and Costs. Emerging Infectious Diseases 2001;7(2):312-318.
http://www.cdc.gov/ncidod/eid/vol7no2/pdfs/pfaller.pdf
"While HSV can be cultured from the CSF of 40% of infants with neonatal HSV CNS disease, the 'gold standard' for virological confirmation of CNS involvement is the polymerase chain reaction (PCR) due to the markedly greater sensitivity of the PCR assay..."4
"The utility of PCR to provide a relative non-invasive means of rapidly establishing an HSE diagnosis has led to its replacing brain biopsy as the 'gold standard' for diagnosis.4