Lung function measurements in children - copsac
Lung function measurements in children - copsac
Lung function measurements in children - copsac
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lung symptoms, 19% said it was the control tw<strong>in</strong> and 27% said both tw<strong>in</strong>s had<br />
comparable symptoms. However, there is a significant risk for recall bias and the MZ<br />
pairs could be mixed up s<strong>in</strong>ce the hospitalization was on average 7 years ago and<br />
parents were generally most unsure of the details. Furthermore, it would be impossible<br />
to make a subgroup analysis restricted to the tw<strong>in</strong> pairs where the parents’ memories<br />
and data agreed. The study group would be very small.<br />
It is known that male sex could be a risk factor for RSV hospitalization (140-142). In<br />
the whole tw<strong>in</strong> cohort the boys had a higher prevalence of severe RSV <strong>in</strong>fection<br />
compared to the girls; odds ratio 1.20; CI [1.07-1.33] as previously presented by<br />
Thomsen et al. (2008) (115), but there was a random overrepresentation of females <strong>in</strong><br />
our study (subgroup).<br />
The discordant MZ tw<strong>in</strong>s <strong>in</strong> our study were born slightly earlier (mean gestational age<br />
35.5 weeks and mean birth weight 2369 grams) than the MZ tw<strong>in</strong>s <strong>in</strong> the overall tw<strong>in</strong><br />
cohort (mean gestational age 36.1 weeks (SD 2.5) and birth weight 2498 grams (SD<br />
549) (115). The differences were small and not significant; therefore it seems that the<br />
discordant tw<strong>in</strong>s were representative of MZ tw<strong>in</strong>s <strong>in</strong> general.<br />
On the other hand it may bias the result because premature <strong>in</strong>fants as a population have<br />
its own risk factors for impaired lung <strong>function</strong>.<br />
The dist<strong>in</strong>ction between possible "wheezers" and “bronchiolitis” may be <strong>in</strong>accurate <strong>in</strong><br />
this as <strong>in</strong> other studies. The dist<strong>in</strong>ction between wheezers and bronchiolitis is normally<br />
related to severity of wheeze and concurrent cl<strong>in</strong>ical signs of lower airway <strong>in</strong>fection.<br />
Our samples <strong>in</strong>cluded the latter, i.e. first hospitalization for severe wheeze with<br />
concomitant signs of lower airway <strong>in</strong>fection.<br />
The highest <strong>in</strong>cidence of hospitalization for RSV-bronchiolitis is often reported <strong>in</strong> the 0-<br />
1-yr-olds (113, 114, 143, 144). However, the reported mean age may be biased from<br />
exclud<strong>in</strong>g older <strong>children</strong> from such analyses. For example Sigurs et al. reported mean<br />
age of RSV hospitalization to be 3.5 months exclud<strong>in</strong>g <strong>in</strong>fants older than 12 months<br />
(98, 98). Fjaerli et al. reported admission age median to be 6 months <strong>in</strong> <strong>children</strong> under<br />
two years old <strong>in</strong> their study (140). One study <strong>in</strong>cluded <strong>children</strong> up to 2 years and<br />
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