Nocturnal dry cough in the first 7 years of life is associated with asthma at school age

Background Childhood wheeze is an important, well-known risk factor for asthma, yet little is known about the contribution of nocturnal dry cough. We investigated the association of nocturnal dry cough at ages 1-7 years with doctor-diagnosed asthma at 8 years of age, both in the presence and absence of wheeze. Methods Data of 3,252 children from the PIAMA birth cohort were studied. Parents reported the presence of nocturnal dry cough, wheeze, and doctor-diagnosed asthma in the past 12 months yearly, from birth up to the age of 8 years. Results Nocturnal dry cough without wheeze was significantly associated with doctor-diagnosed asthma at age 8, except for age 1 (range of Relative Risks (RR) at ages 2-7: 1.8 (age 5) - 7.1 (age 7), all P-values <0.048). As expected, wheeze without nocturnal dry cough was strongly associated with doctor-diagnosed asthma at age 8 (range of RR: 2.0 (age 1) - 22.2 (age 7), all P-values <0.003). Of interest, nocturnal dry cough with wheeze showed the strongest association with doctor-diagnosed asthma at age 8 (range of RR: 3.7 (age 1) - 26.0 (age 7), all P-values <0.001). The relative excess risk of asthma at age 8 due to interaction of nocturnal dry cough with wheeze at age 1 year was 1.8 (0.1-3.6, P<0.01). Conclusion Nocturnal dry cough and wheeze in early childhood are both independently associated with asthma at school age. The presence of both nocturnal dry cough and wheeze at age 1 almost doubles the risk of asthma at age 8 compared to wheeze alone.

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