Discussion
Identifying the factors increasing the risk of development of severe
bronchiolitis in patients without chronic disease is important in terms
of standardizing the frequency of follow-ups of bronchiolitis patients
and hospitalization indications, and the decision to intervene early in
at-risk patients. The purpose of the present study was to determine
individual, familial, and environmental predictive risk factors for the
development of severe bronchiolitis in healthy-appearing cases of acute
bronchiolitis with no previous history of chronic disease.
In a study of children with bronchiolitis requiring mechanical
ventilation, Mansbach et al.6 found that 61% of cases
assessed as severe bronchiolitis and given respiratory support with CPAP
or intubation were boys, and 39% were girls. Robledo-Aceves et
al.3 investigated risk factors for severe
bronchiolitis in the emergency department and observed that 60.5% of
severe bronchiolitis cases were boys. Similarly in the present study,
boys constituted 60% of the cases valuated as severe bronchiolitis, and
girls 40%, no statistically significant difference being observed with
the mild-moderate patient group.
Robledo-Aceves et al.3 reported a mean age of 6.60
months in their cases of severe bronchiolitis, but observed no
significant difference compared to the control group. Mansbach et
al.6 a significantly higher mechanical ventilation
requirement in the first six months, and especially in patients younger
than two months, compared to the control group. In their study of risk
factors for respiratory decompensation, Dadlez et al.8reported a mean age of 4.2 months in a group developing respiratory
failure and 7.2 months in a group with no respiratory failure, the
difference being statistically significant. They authors also identified
age less than six months as a significant predictor of respiratory
decompensation. In the present study, the mean age of the cases with
severe bronchiolitis was 6.50 months, and that of the mild-moderate
bronchiolitis cases was 6.07, the difference not being statistically
significant.
Dadlez et al.8 determined no statistically significant
difference in weight-for-age z-scores between groups developing and not
developing respiratory failure. Weight-for-age z-scores of -0.87 in
cases of severe bronchiolitis and -0.30 in mild-moderate cases were
determined in the present study (p<0.001). In addition,
multivariate logistic regression analysis identified a low
weight-for-age z-score as an independent predictor of development of
severe bronchiolitis, increasing the risk of development 0.56-fold.
In a study of the severity of respiratory syncytial virus (RSV)
infection and breastfeeding, Nishimura et al.9determined a more severe clinical course among non-breastfed young
infants, and reported that breastfeeding exhibited a protective effect.
Mansbach et al.6 determined a history of breastfeeding
in 57% of cases of severe bronchiolitis and in 61% of a control group,
although the difference was not statistically significant. Similarly in
the present study, a history of breastfeeding only was present in 74.1%
of cases in the severe bronchiolitis group, and in 75.2% of the
mild-moderate group, the difference also not being statistically
significant.
Semple et al.10 reported a mean gestation time of 35.8
weeks in cases requiring mechanical ventilation support compared to 38
weeks in a control group, the difference being statistically
significant. Coşkun et al.11 investigated risk factors
for intensive care requirements among children with bronchiolitis and
determined a mean gestation period of 37.9 weeks in a group followed-up
in intensive care and of 38.2 weeks in a control group, the difference
not being significant. Mean gestation in the severe bronchiolitis group
in the present study was 38.2 weeks, compared to 38.3 weeks in the
mild-moderate bronchiolitis group. The difference was not significant
(p=0.602).
Mansbach et al.6 reported a previous history of
bronchiolitis attacks in 19% of severe bronchiolitis cases and in 23%
of a control group, the difference not being significant. In the present
study, a previous history of bronchiolitis attacks was observed in
36.5% of severe bronchiolitis cases, significantly higher than in
mild-moderate cases at 27.1% (p=0.004). At multivariate logistic
regression analysis, a history of frequent previous bronchiolitis
attacks emerged as an independent predictor of severe bronchiolitis
development, increasing the risk 1.84-fold.
Mansbach et al.6 reported no significant difference in
familial history of asthma, being observed in 32% of a severe
bronchiolitis group and 31% of a control group. A family history of
asthma was determined in 9.5% of the severe bronchiolitis group and
11.6% of the mild-moderate bronchiolitis group, and the difference was
not significant (p=0.240).
Hasegawa et al.12 investigated risk factors
necessitating intensive care are reported exposure to cigarette smoke in
17% of patients transferred to intensive care due to clinical worsening
and in 13% of a control group. The difference was not significant.
Mansbach et al.6 reported exposure to cigarette smoke
in 11% of a group with severe bronchiolitis and in 13% of a control
group. The difference was significant. Robledo-Aceves et
al.3 described exposure to cigarette smoke as a single
independent risk factor associated with severe bronchiolitis. In the
present study, rates of exposure to cigarette smoke associated with
active maternal smoking were 20% in the severe bronchiolitis group and
11.3% in the mild-moderate group, and the difference was statistically
significant (p=0.046). However, exposure to cigarette smoke was not
identified as an independent predictor of severe bronchiolitis
development at multivariate logistic regression analysis.
Mansbach et al.6 reported an independent association
between maternal smoking during pregnancy and severe bronchiolitis
requiring CPAP and/or intubation. Robledo-Aceves et
al.3 determined smoking during pregnancy in 7.5% of
the severe bronchiolitis group and 6.7% of the mild-moderate group, the
difference being insignificant. Rates of maternal smoking during
pregnancy in the present study were 16.5% in the severe bronchiolitis
group and 9% in the mild-moderate group. The difference was also not
significant (p=0.050).
Coşkun et al.11 reported a higher number of siblings
among a group followed-up in intensive care compared to a control group,
although the difference was not significant. In the present study,
12.9% of severe bronchiolitis cases and 26.5% of mild-moderate cases
were only children (p=0.010). However, this did not emerge as an
independent predictor of severe bronchiolitis development.
Robledo-Aceves et al.3 reported that 71.6% of a
severe bronchiolitis group and 42.5% of a control group lived in
crowded conditions, and that this was linked to severe bronchiolitis.
The number of members of the household in the present study was higher
in the severe bronchiolitis group than in the mild-moderate group
(p=0.011). However, this did not emerge as an independent predictor of
severe bronchiolitis at multivariate logistic regression analysis.
Mansbach et al.6 reported a significantly higher rate
of reduced feeding in the severe bronchiolitis group, at 63%, compared
to 41% in the control group. They also reported an independent
association between reduced feeding and severe bronchiolitis requiring
mechanical ventilation. Rates of oral feeding in the present study were
76.5% in the severe bronchiolitis cases and 62% in the mild-moderate
bronchiolitis cases (p=0.016). However, this did not emerge as an
independent predictor of severe bronchiolitis at multivariate logistic
regression analysis.
Semple et al.10 reported times between onset of
symptoms and admission to hospital of 3.1 days in a group developing
respiratory insufficiency receiving mechanical ventilation support, of
3.6 days in a group given oxygen support only, and of 4.2 days in a
group not given oxygen support, although the difference was not
statistically significant. DeVincenzo et al.13reported an approximate time of four days between onset of symptoms and
admission, but did not evaluate this as significant in terms of
intensive care requirement and respiratory insufficiency. The relevant
findings in the present study were 4.04 days in the severe bronchiolitis
group and 4.90 days in the mild-moderate bronchiolitis group (p=0.017).
A short time between onset of symptoms and admission was identified as
an independent predictive parameter in the development of severe
bronchiolitis, increasing the risk of severe bronchiolitis 0.62-fold.
Hasegawa et al.12 reported similar onset durations of
respiratory difficulty, one of the findings of clinical worsening,
between a group requiring intensive care and another with no such
requirement. In Mansbach et al.’s study6, 39% of
severe bronchiolitis cases experienced respiratory difficulty for less
than one day before presentation, compared to 26% of the control group,
and an independent association was determined with mechanical
ventilation requirement. In the present study, the time elapsing between
onset of symptoms and worsening of findings was 2.78 days in the sever
bronchiolitis group and 4.29 days in the mild-moderate group
(p<0.001). However, this did not emerge as an independent
predictive parameter in the development of severe bronchiolitis at
multivariate logistic regression analysis.
Tourniaire et al.14 investigated whether Hb
concentrations were a factor in clinical worsening, and reported mean Hb
values of 11.1 g/dL in a group with severe bronchiolitis and 12 g/dL in
a control group, the difference being statistically significant. They
also determined that cases Hb values lower than 10 g/dL resulted in
long-term respiratory support requirements. Mean Hb values in the
present study were 10.83 g/dL in the severe bronchiolitis group and
11.19 g/dL in the mild-moderate group (p=0.021). Low Hb values also
emerged as an independent predictive parameter in severe bronchiolitis
development at logistic regression analysis, increasing the risk of
severe bronchiolitis 0.72-fold. We think that low Hb may result in
worsening of the manifestation in bronchiolitis patients by reducing
oxygen transport capacity.
In conclusion, we observed a higher risk of severe bronchiolitis
development in individuals with a low weight-for-age z-score, with a
short time elapsing between onset of symptoms and admission, with a
larger number of previous attacks, and with low hemoglobin. We think
that consideration and identification of these risk factors will serve
as a guide to clinicians in the early determination of cases of severe
bronchiolitis.