Infectious Disease Testing of Immune Compromised Patients
Two of the largest segments of infectious disease testing in immune compromised patients are solid organ transplant (SOT) and bone marrow transplant (BMT) patients. There are currently 27,000 solid organ and 18,000 bone marrow transplants performed annually in the U.S. with 170,000 long-term solid organ transplant patients. The U.S. accounts for 50% of the total worldwide transplant population. All patients who have undergone transplants are given immune-suppressive drug therapy and are as a result more susceptible to viral and fungal diseases.
Viral Diagnostic Market Opportunity
Introduction of effective immunosuppressive drugs in the 1980’s had a profound impact on the success and adoption of organ transplants to treat end-stage organ diseases. However, side-effects from drug-induced immunosuppression are common and must be carefully monitored and managed throughout the lifetime of the patient. Nearly half of newly transplanted patients are diagnosed with infections, typically viral, in the first 3 to 6 months following surgery. Due to their drug-induced immune suppressed state, viral diseases are more common and serious in these patients compared to healthy individuals. A number of these viral infections can pose grave consequence for transplant patients including allograft rejection. Viral diseases can result via transmission from the donor tissue, exposure to the environment or more typically, reactivation of the patient’s own latent viruses. The viruses of most concern to transplant patients vary with the organ transplanted although cytomegalovirus (CMV) and Epstein-Barr virus (EBV) are of universal concern. Hepatitis B and C viruses are commonly associated with liver transplant patients whereas the polyoma viruses such as BKV are most problematic for kidney transplants. Recently, attention has focused on better understanding the role of human herpesviruses (HHV6) and (HHV7) infections and whether their co-infection with other viruses such as CMV has a role in determining the course and severity of disease.
Current Diagnostic Testing Practices
Current testing frequency varies. Certain centers test immediately after the transplant and initiate prophylactic antiviral drug therapy regardless of viral levels, although this practice has its issues due to the significant cost of anti-viral drugs, the drug side-effect risks, and the concern of evolving drug resistance. Some centers will request testing if symptoms of infection become evident and will continue to monitor patients several times a week while the treatment protocol is being established. Other centers will monitor patients at risk (test several times per week) and preemptively initiate anti-viral therapy when an increase in viral load is detected although clinical symptoms may not yet be present. The consensus is that 10 to 20 diagnostic tests per patients for major transplant-associated viruses are performed in the first year and 1 – 3 tests per year thereafter.
Need for quantitative multiplexed diagnostic test
Quantitative, rather than qualitative, molecular-based data are essential for the management of transplant patients as most of these herpes and polyoma viruses are common in the human population and will persist for the life of the individual in a dormant and asymptomatic state. Since increasing viral loads often correlate with conditions that signal potential organ rejection serial, quantitative (viral load type) assays are essential to guide therapy. Quantitative assays are also used to monitor patients and initiate anti-viral therapy in a pre-emptive manner when rise in viral load is detected but before symptoms of infection become apparent. CMV is currently the most frequently ordered test for both Solid Organ Transplant (SOT) and Bone Marrow Transplant (BMT) patients based on historical data to suggest its problematic nature. However, publications have shown that other viruses are prevalent and problematic, and that patients can be co-infected with two or more viruses.
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