In medicine, it is often assumed that children are "just miniature versions of adults," said Jennifer Dien Bard, director of the Laboratory for Clinical Microbiology and Virology at Los Angeles Children's Hospital. “But they're not just little adults. It is really important that all tests available offer specific strategies for children and their specific needs. "
In the rush to make treatments, vaccines, and diagnostics available for widespread use, companies often neglect the inclusion of children in early studies testing whether products or therapies are safe and effective. Tests for viruses, bacteria, and other infectious microbes that give great results for adults, however, don't always translate perfectly for children.
The reasons for these differences aren't always obvious, said Dr. Pollock. For example, children's immune systems may be better able to locate and bind to certain infectious invaders, making them more difficult to detect using standard tests.
In a study published in the Journal of Clinical Microbiology in October, Dr. Pollock and her team received data from nine children's hospitals across the country, all of which reported relatively low virus counts in children with no symptoms. Another, not yet published in a peer-reviewed scientific journal, suggested a similar trend in sick children.
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Things to know about testing
Confused by Coronavirus Testing Conditions? Let us help:
- antibody: A protein produced by the immune system that can recognize and attach to certain types of viruses, bacteria or other invaders.
- Antibody test / serology test: A test that detects antibodies specific to the coronavirus. About a week after the coronavirus infects the body, antibodies begin to appear in the blood. Because antibodies take so long to develop, an antibody test cannot reliably diagnose an ongoing infection. However, it can identify people who have been exposed to the coronavirus in the past.
- Antigen test: This test detects parts of coronavirus proteins called antigens. Antigen tests are quick and only take five minutes. However, they are less accurate than tests that detect genetic material from the virus.
- Coronavirus: Any virus that belongs to the Orthocoronavirinae virus family. The coronavirus that causes Covid-19 is known as SARS-CoV-2.
- Covid19: The disease caused by the new coronavirus. The name stands for Coronavirus Disease 2019.
- Isolation and quarantine: Isolation is separating people who know they have a contagious disease from those who are not sick. Quarantine refers to restricting the movement of people who have been exposed to a virus.
- Nasopharyngeal smear: A long, flexible rod with a soft swab that is inserted deep into the nose to collect samples from the space where the nasal cavity meets the throat. Samples for coronavirus tests can also be taken with swabs that don't go as deep into the nose – sometimes called nasal swabs – or with swabs from the mouth or throat.
- Polymerase chain reaction (PCR): Scientists use PCR to make millions of copies of genetic material in a sample. With the help of PCR tests, researchers can detect the coronavirus even when it is scarce.
- Viral load: The amount of virus in a person's body. In people infected with the coronavirus, viral loads can peak before symptoms, if any.
Laboratory tests, such as those using a technique known as the polymerase chain reaction, or P.C.R. are sensitive enough to detect these low-level infections, said Dr. Pollock. However, the virus may not be present in sufficient quantities to be detected by a rapid test, for example those that only detect relatively large amounts of antigens or parts of coronavirus proteins. The Binax NOW is one such test.
Many such children "will be negative on rapid tests," said Dr. Pollock. "It affects how we think about school environments and day care."
Some children may naturally tend to harbor fewer viruses. It was also possible that the children in these studies were all sampled too late in their infections, when the virus was already extinct. If that were the case, Dr. Pollock, these children might have transmitted, or even transmitted, the virus in large quantities at one point, but were not tested during that time. Telling these scenarios apart could be difficult without testing many more children, she said.