People who suffered acute COVID-19 infection are more likely to experience prolonged cough and sputum production as part of long-term COVID, according to a Japanese study.

Multiple prolonged symptoms are observed in patients who recover from acute COVID-19, defined as long COVID-19.

Cough and sputum are presented by patients with long COVID during the acute and post-acute phases. The study, published in the journal Respiratory Research, aimed to identify specific risk factors for cough and sputum in patients with long-term COVID-19.

Researchers from Keio University in Tokyo enrolled hospitalised patients with COVID-19 aged 18 years from 26 medical institutions.

At the three-, six---, and 12-month follow-ups, there were no differences in the incidence rates of wet and dry coughs. However, the proportion of patients producing sputum without coughing rose over time compared with those with both sputum production and coughing.

At all follow-up visits, analyses of cough and sputum production identified the risk factors for persistent symptoms as the use of intermittent mandatory ventilation (IMV), smoking, and older age.

At 12 months, severe COVID-19 was associated with cough and sputum production based on imaging findings, kidney and liver abnormalities, pulmonary blood clots, and higher levels of lactate dehydrogenase (indicating organ or tissue damage), Krebs von den Lungen-6 (indicating lung inflammation or damage), and haemoglobin A1c (indicating elevated blood glucose).

“These findings emphasise that a preventive approach including appropriate vaccination and contact precaution and further development of therapeutic drugs for COVID-19 are highly recommended for patients with risk factors for severe infection to avoid persistent respiratory symptoms,” the researchers said.

Long-term persistent cough and sputum are burdens on patients after recovery from acute COVID-19. Further investigations are needed to elucidate the underlying mechanisms and develop specific therapeutic drugs for these persistent symptoms in patients with long COVID, the researchers said.