Predicting the duration of symptoms in lower respiratory tract infection

Acute lower respiratory tract infection (LRTI) presenting in primary care has a long natural history. Antibiotic treatment makes little or no difference to the duration of cough. Limited information is currently available regarding predictors of illness duration.

To determine predictors of illness duration in acute LRTI in primary care.

Secondary analysis of trial data to identify independent predictors of illness severity and duration.

Primary care.

Eight-hundred and seven patients aged 3 years and over with acute illness (21 days or less) presenting with cough as the main symptom plus at least one symptom or sign from sputum, chest pain, dyspnoea, or wheeze were recruited to the study. Main outcomes were duration of symptoms (rated at least a slight problem) and more severe symptoms (rated at least moderately bad).

The average duration of cough (rated at least a slight problem) was 11.7 days and was shorter among children (duration -1.72 days; 95% confidence interval [CI] = -3.02 to -0.41) or in individuals with a history of fever (-1.22 days; 95% CI = -0.18 to 2.27). The duration of cough was longer among those with restricted activities on the day they saw the doctor (+0.69 days for each point of a 7-point scale). The duration of more severe symptoms was longer in those with a longer duration of symptoms prior to consultation, with a more severe cough on the day of seeing the doctor, and restriction of activities on the day of seeing the doctor.

Illness duration may be predicted from a limited number of clinical symptoms and from prior history. These findings should be subjected to validation in a separate population. To minimise expectation about rapid resolution of illness, adults who have restricted activities could be advised that they are likely to experience symptoms for longer.