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Editor,—Rona et al 1 have related sleep disturbance to sociocultural factors associated with ethnicity and respiratory illness and concluded that these are important risk factors for sleeping disorders in childhood. We have recently completed a study examining the relation between nighttime cough and sleep in inner city children,2 and found that although there is an association, it is very weak (regression coefficient 0.13, SE 0.036). Of 96 subjects eligible for the study, 65 (67%) were child co-sleepers or room sharers, 32 (33%) were from social class V, and English was not the first language of 29 (30%) families. We filmed children in their homes.3 Sleep behaviour was compared with the only other study using an objective measure of sleep. This was in a Canadian university town.4No difference was found in the number of awakenings (median = 3), although the total length of time asleep (10 hours) was one hour longer than our children’s sleep (9.1 hours). Sleep then seems to be similar across classes even though our children were coughing.
In a pilot study looking at the perception of respiratory symptoms, we asked 20 parents of recurrently wheezy children “How do you know when your child is wheezy?”, and 13 gave as the main reason “because he/she coughs”. Could the subjects in the study by Rona et al be considered wheezy because their parents heard them cough? Parents are not good at judging sleep and nocturnal respiratory symptoms in children when compared with objective measures,5 6 and obviously parents are asleep for part of the night themselves. It could be that some of Ronaet al’s observations reflect parental wakening because of their children’s cough rather than wheeze, and because of their own sleep disturbance.7 Cough is better associated with atmospheric pollution than wheeze, which is related to atopy.8 Poor atmospheric conditions and overcrowding could cause children’s cough and parental sleep disturbance. In summary, difficulties in sleep due to what parents perceive as “wheeze” could be considered normal waking in children as our study suggested. We believe there is a need for more objective observation of what goes on at night in families’ homes.