Nasal nitric oxide is decreased in acute mild COVID-19 and related to viral load

Gaseous nitric oxide levels from the lungs (FeNO) and from the nose (nNO) have been demonstrated to react to acute infection or influenza vaccination. There are no published data on nNO levels during acute COVID-19, but normal levels of FeNO have been reported in one study. Our aim was to assess if acute mild COVID-19 alters nasal or bronchial NO output at the time of acute infection and at a two-month follow up, and if this is related to symptoms or viral load. This study included 82 subjects with mild acute airway infection who did not need hospitalization: 43 cases (reverse transcription polymerase chain reaction (RT-PCR)-positive for SARS-CoV-2 in routine testing from nasopharynx) and 39 age- (±5 years) and gender-matched controls (RT-PCR-negative for SARS-CoV-2). During acute infection, the cases had lower nNO compared to controls (158 [104-206] vs. 232 [203-279] nl min^-1;p< 0.001), but after two months, there was no significant difference between the groups (230 [179-290] vs. 268 [222-320] nl min^-1;p= 0.162). There was no difference in FeNO between the groups at either of the visits. Nasal NO correlated with the cycle threshold (Ct) value of the nasopharyngeal RT-PCR test for SARS-CoV-2 (Spearman'sr_s= 0.550;p< 0.001), that is, nNO was lower with a higher viral load. Nasal NO output was decreased in acute COVID-19 in relation to higher viral load, suggesting that the type and intensity of inflammatory response affects the release of NO from airway mucosa. In these subjects without significant lower airway involvement, there were no clinically relevant findings regarding FeNO.