Cytomegalovirus (CMV) is a common virus belonging to the herpesvirus family that can infect people of all ages. In most healthy individuals, CMV infection is usually asymptomatic or causes only mild, flu-like symptoms. Once acquired, the virus remains latent in the body for life, but it can reactivate if the immune system is suppressed. Testing for CMV status is a routine procedure in specific medical situations, such as during pregnancy or before an organ transplant. This testing helps medical professionals assess the risk of severe illness in vulnerable populations.
Understanding the CMV Negative Result
A “CMV negative” test result indicates that an individual has not previously been exposed to the virus and is therefore seronegative. Seronegativity means the body has not produced the specific Immunoglobulin G (IgG) antibodies that signal a past infection. Testing for CMV status typically looks for these IgG antibodies in the blood, and their absence defines the negative status.
Since the body has no pre-existing immune defense, a CMV negative person remains susceptible to a primary, or first-time, CMV infection. This susceptibility is a significant factor in clinical settings, as a primary infection carries a higher risk of complications than viral reactivation. In contrast, a CMV positive result signifies prior exposure and the development of lifelong antibodies. This seronegative status shifts the focus from managing a latent virus to preventing an initial encounter.
How CMV Spreads and Who is at Risk
CMV is transmitted through close, prolonged contact with infectious bodily fluids, including saliva, urine, blood, semen, tears, and breast milk. Transmission does not typically occur through casual contact, but rather through activities like sharing food, utensils, or through sexual contact. The virus is commonly shed in saliva and urine, often for months, even after the infected person no longer shows symptoms.
A major route of exposure for adults is contact with young children, who frequently shed the virus in high concentrations. People regularly around toddlers, such as parents and daycare workers, have an increased risk of exposure. Healthcare professionals are also considered a higher-risk group due to potential exposure to patient fluids. Transmission can also happen through blood transfusions or organ transplants from an infected donor to a CMV-negative recipient.
Primary Infection Risk During Pregnancy
For individuals who are CMV negative, the greatest concern is the risk of acquiring a primary infection during pregnancy. A first-time CMV infection in a pregnant person carries the highest risk of transmitting the virus to the developing fetus, resulting in congenital CMV. The risk of transmission to the fetus can be as high as 40 to 70% if the infection is acquired in the third trimester, though the risk of severe fetal damage is highest in the first or second trimesters.
Congenital CMV is the most common infectious cause of birth defects and can lead to various long-term health problems for the child. Potential outcomes include hearing loss, vision problems, and developmental delays. Although only about 1 in 5 babies with congenital CMV will show long-term health issues, the severity of a primary infection makes prevention a high priority for seronegative pregnant individuals.
To mitigate this risk, preventative hygiene practices are recommended, especially when interacting with young children. These measures include frequent handwashing for at least 15 to 20 seconds, particularly after changing diapers or wiping a runny nose. Individuals should also avoid sharing food, drinks, or eating utensils with young children to minimize contact with saliva.
Importance in Blood and Organ Donation
CMV status is a significant factor in transfusion and transplantation medicine, aiming to prevent the transmission of the virus to patients with compromised immune systems. CMV negative blood components, such as red blood cells and platelets, are reserved for highly vulnerable recipients who are also CMV negative. These at-risk patients include premature infants, newborn babies, and individuals undergoing cancer treatment or receiving organ transplants.
Transfusing CMV positive blood products to a CMV negative, immunocompromised patient can result in a severe primary infection. A process called leukoreduction, which filters out the white blood cells where CMV resides, is often used to make blood products “CMV-safe” for most patients. However, CMV negative blood is still preferred for the most susceptible patients, as it offers the lowest possible risk of transmission.
In organ transplantation, the CMV status of both the donor and the recipient is a factor in pairing decisions. A CMV negative recipient ideally receives an organ from a CMV negative donor to prevent a primary infection, which can lead to serious complications and organ rejection. If a negative recipient must receive an organ from a positive donor, they often require prophylactic antiviral medication to manage the risk of acquiring the virus.