Because of the COVID-19 pandemic and the threat of many other infectious diseases, scientists have begun looking more closely at what causes diseases to spread and what characterizes a person’s infection. One of the metrics that has received increased focus is the number and impact of asymptomatic cases in the general population.
Asymptomatic is a term used by everyone from physicians to parents to refer to someone who is not showing symptoms of an illness they may have or an illness they may have had at one point. The prefix "a" is from the Greek for "not", so "asymptomatic" means not symptomatic.
A doctor may refer to a person as asymptomatic when they’ve had an illness but do not experience symptoms. As many as 40% of cases of COVID-19 are asymptomatic, according to research studies. These individuals may not show symptoms, but CT-scans reveal abnormal findings. Simply put, a disease may be silent, but maybe not harmless. Many illnesses, including the flu, HIV, and even cancer, can go undetected for a long time due to a person being asymptomatic.
Doctors are continually looking into the role of asymptomatic infections in public health crises. By one study’s estimate, as many as 28% of flu cases may be asymptomatic. However, this is a difficult metric to measure. Asymptomatic infections or diseases may be detected early through blood work, although this research is also in its early phases.
Presymptomatic is different than asymptomatic. Presymptomatic means that a person is carrying an illness but not yet showing symptoms; however, they will show symptoms eventually. Asymptomatic people never show symptoms at any time during their illness. As such, both terms will generally be applied retroactively.
It’s possible that genetics influence whether or not a person becomes symptomatic when dealing with a certain disease. For example, research on older adults with Alzheimer’s found that genetics could determine some of the variances between people who show symptoms and those who don’t. The same appears to go for other diseases such as COVID-19.
For some diseases, there is evidence that people without symptoms can still transmit the illness. For conditions like the flu, however, studies offer contrasting viewpoints. Some researchers have found that asymptomatic carriers have no impact on transmission, while others have found a significant impact.
The viral load is the amount of a specific virus found in a test sample taken from an infected individual. This amount tells a doctor how readily a virus is replicating. Scientists cannot always predict an illness' severity based on the viral load alone, however. For example, some studies show severe cases of COVID-19 pneumonia were linked with higher viral loads. Yet, other studies revealed that some asymptomatic patients had similar viral loads to those who experienced symptoms. More research is needed to better understand COVID-19.
Since the research on whether or not an asymptomatic person can infect others is still in its infancy, everyone who is suspected of carrying an illness should take precautions for their own health and the health of others. This includes getting tested for the specific disease and seeking the right forms of treatment.
Cancer, while often identified through symptoms such as unusual bleeding and changed bowel habits, can also occur pre-symptomatically. Most people with cancer in its early stages will be asymptomatic, and testing for these diseases might be difficult. Since symptoms of certain cancers like lung cancer are often late-onset, there are limited treatment options. However, the method of testing for cancers via bloodwork or other screening tests appears promising in the efforts to catch cancer early.
Some STDs, such as syphilis, don’t show symptoms until the infection has progressed to a serious point. By one estimate, 50% of syphilis infections are asymptomatic, which presents a real danger for infected people and their partners. While identifying these asymptomatic infections is hard, preventing them is often as simple as being tested regularly and practicing safe sex.
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