SINGAPORE - Two Covid-19 patients in Singapore who tested positive for dengue were found later to not have the mosquito-borne disease.

One was a 57-year-old woman, who was said to be the first patient in Singapore to have contracted both the coronavirus and dengue. The other is a man, also aged 57.

These details were disclosed in a paper published in The Lancet medical journal last week (March 4), authored by a group of doctors from the National University Health System, Ng Teng Fong General Hospital, polyclinics and the Environmental Health Institute.

The doctors said the two cases highlighted the importance of recognising false-positive dengue results in patients with Covid-19. Those with dengue typically have a fever and a rash, but unlike Covid-19 patients, they do not have such respiratory symptoms as a runny nose, cough or sore throat.

"Failing to consider Covid-19 because of a positive dengue rapid test result has serious implications not only for the patient but also for public health," said the authors.

"We emphasise the urgent need for rapid, sensitive and accessible diagnostic tests for Sars-CoV-2, which need to be highly accurate to protect public health." Sars-CoV-2 is the new coronavirus that causes the Covid-19 disease.

As of February, 3,264 dengue cases were reported in Singapore this year.

At least 160 people have fallen ill in Singapore because of the coronavirus.

Both patients in the paper had tested positive for dengue and were treated as dengue patients, until they were found to have contracted the coronavirus.

The man had visited a hospital on Feb 9 with a cough, fever and a low blood platelet count. He tested negative for dengue and was discharged, but visited another healthcare clinic when his symptoms worsened.

A second test for dengue came back positive, and the man was referred to a hospital for dengue and a worsening cough. He also had difficulties breathing.

The man was subsequently found to have Covid-19, and repeated tests for dengue came back negative.

Like him, the woman had tested positive for dengue when she went to a hospital on Feb 13 with a mild cough, fever, diarrhoea and muscle pain. She was discharged to be treated as an outpatient.

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But she returned two days later when her symptoms worsened, and was admitted into a hospital as a dengue patient. She had difficulty breathing three days after her admission, and was tested positive for the coronavirus. Doctors repeated a dengue test on her which turned out negative, and an earlier blood sample of hers was also negative.

This confirmed the false positive dengue results, said the authors in their paper.