Serum lactate hydrogenase concentrations were significantly higher in the ten participants who were asymptomatic on admission but developed symptomatic COVID - 19 compared with the 33 participants who remained asymptomatic throughout the observation period ( five [ 50 % ] vs four [ 12 % ] participants ; odds ratio 7 · 25 , 95 % CI 1 · 43 - 36 · 70 ; p = 0 · 020 ) .