Those with a history of significant comorbidities experienced a significantly greater reduction in symptom severity between days 2 and 4 ( interaction term -0.28 , P = 0.003 ; estimated effect of antibiotics among those with a past history -0.28 [ 95 % confidence interval = -0.44 to -0.11 ] , P = 0.001 ) , equivalent to three people in 10 rating symptoms as a slight rather than a moderately bad problem .