(Reuters) – A study looking at 10 Chinese children who were infected with the novel coronavirus has uncovered evidence that COVID-19, the respiratory disease it causes, can appear as a less-serious infection, illustrating how difficult the infection can be to detect based only on symptoms.

The study led by Chinese researchers, published on Friday in the journal Nature Medicine, found that one of the children showed no symptoms at all and the rest had mild symptoms.

The researchers also found that the virus itself can continue to appear in fecal samples long after nose and throat swabs no longer show evidence of an infection. Rectal swab testing may be a more effective way to determine how long to quarantine children, the researchers said.

The only reason the 10 children – six boys and four girls ranging in age from two months to 15 years – were tested at a hospital in the city of Guangzhou was because they were family members of COVID-19 patients or had close contact with people diagnosed with the disease, not because medical care had been sought for them, the researchers said.

Five of the children had a cough, four had a sore throat, three had diarrhea and two had nasal congestion and runny nose, symptoms that the researchers said could can make COVID-19 look like other illnesses.

“Mild and atypical presentations of the infection in children may make it difficult to detect,” according to the study, whose lead author was Dr. Yi Xu of Guangzhou Women and Children’s Medical Center in Guangzhou.

In all, 745 children deemed as “highly suspected” of being infected were screened between Jan. 22 and Feb. 20. Of that group, 1.3% were found to be infected.

The low ratio follows the pattern described by researchers in another study published on Thursday in The New England Journal of Medicine in which a separate team of Chinese doctors reporting out of the city of Wuhan found that only 1.6% of respiratory infections among hospitalized children were COVID-19. The outbreak emerged last December in Wuhan and the virus has since spread to various parts of the world.

In this latest study, seven of the 10 children had a fever, although it was never higher than 39 degrees C (102.2 F).

None had the pneumonia that has made the disease deadly in some adults, although CT scans showed that five of the 10 children had isolated or multiple patchy “ground-glass” patches, usually in the outer lung fields.

The headache, muscle aches, nausea, lethargy, labored breathing, vomiting and disorientation that can be seen in adults who have COVID-19 were all absent in this small group of infected children, the researchers said.

The researchers cautioned that although the virus was persistently found in the rectal swabs of eight of the 10 children even after it had vanished from nose and throat swabs, it was not clear if the virus particles present in the feces were infectious.

(Reporting by Gene Emery; editing by Nancy Lapid, Caroline Humer and Will Dunham)