Does atopy affect the course of pneumonia? Allergic Airway Inflammation and Susceptibility to Pneumonia
Widodo Judarwanto, pediatrician
The presence of atopy is considered as a risk factor for severe respiratory symptoms in children. The objective of this study was to examine the effect of atopy on the course of disease in children hospitalised with viral pneumonia. The relationship between allergic airway inflammation and pneumococcal pneumonia is not well understood.
Kang et all studied susceptibility to experimental pneumococcal pneumonia in mice with and without allergic airway inflammation. Susceptibility to pneumococcal pneumonia was evaluated by challenging mice with a bioluminescent Streptococcus pneumoniae strain after sensitization with ovalbumin (OVA), with subsequent monitoring of pneumococcal infection using real-time photonic imaging. Of 46 OVA-sensitized mice challenged with pneumococci, 13 (28%) developed imaging findings consistent with pneumococcal pneumonia. In comparison, 28 (57%) of 49 non-sensitized control mice developed pneumococcal pneumonia (P = 0·005). While none of the control group developed meningitis (0%, none of 28), two mice in the OVA-sensitized group developed meningitis (15·4%, two of 13) (P = 0·09). The mean bacterial count in the lung was significantly lower in the OVA-sensitized than the non-sensitized group (8·26 ± 0·69 versus 9·21 ± 0·67 log10 colony-forming units (CFU)/g, P = 0·002). There was a trend towards the mean bacterial count in the spleen being higher in the OVA-sensitized versus the non-sensitized group (8·14 ± 0·89 versus 7·45 ± 1·07 log10 CFU/g, P = 0·071). A high level of interleukin (IL)-4 in lung homogenates was associated with risk of pneumococcal infection independent of sensitization with OVA (odds ratio: 49·7, 95% confidence interval 2·92-846·5, per increment of 1·0 pg/ml). In the murine model studied, acute allergic airway inflammation reduced susceptibility to pneumococcal pneumonia. IL-4 may increase the risk of pneumococcal pneumonia independently of allergic airway inflammation.
Talbot et al.reported recently that asthma is associated with an increased risk of IPD among Medicaid recipients of the state of Tennessee. This study finding was confirmed independently in our recent study in Rochester, Minnesota. Higher rates of pneumococcal nasopharyngeal colonization as well as sinusitis and otitis media have been reported among individuals with asthma. The Advisory Committee on Immunization Practices has recommended recently that adults with asthma receive the pneumococcal vaccine. The mechanisms underlying the above observations are unknown. T helper type 2 (Th2)-predominant immune responses to various environmental stimuli play a role in the development and exacerbation of atopic diseases, including asthma. Numerous studies demonstrate that Th2 cytokines [e.g. interleukin (IL)-4)] down-regulate Th1 functions; this has been suggested to be associated with susceptibility to and severity of protozoal, mycoplasmaa, bacterial, viral and candidal infections. Despite evidence that Th2 cytokines increase susceptibility to these infections, whether Th2 immune responses (i.e increased Th2 cytokines or reciprocal counter-regulation of Th1 cytokines) influence susceptibility to IPD is unknown.
Erdem et all reported children between the ages of 1 and 6 years hospitalised due to viral pneumonia between the years of 2013 and 2016 were included to this multicentre study. Patients were classified into two groups as mild-moderate and severe according to the course of pneumonia. Presence of atopy was evaluated with skin prick tests. Groups were compared to evaluate the risk factors associated with severe viral pneumonia. A total of 280 patients from nine centres were included in the study. Of these patients, 163 (58.2%) were male. Respiratory syncytial virus (29.7%), Influenza A (20.5%), rhinovirus (18.9%), adenovirus (10%), human metapneumovirus (8%), parainfluenza (5.2%), coronavirus (6%), and bocavirus (1.6%) were isolated from respiratory samples. Eighty-five (30.4%) children had severe pneumonia. Atopic sensitisation was found in 21.4% of the patients. Ever wheezing (RR: 1.6, 95% CI: 1.1-2.4), parental asthma (RR: 1.5, 95% CI: 1.1-2.2), other allergic diseases in the family (RR: 1.8, 95% CI: 1.2-2.9) and environmental tobacco smoke (RR: 1.6, 95% CI: 1.1-3.5) were more common in the severe pneumonia group. When patients with mild-moderate pneumonia were compared to patients with severe pneumonia, frequency of atopy was not different between the two groups. However, parental asthma, ever wheezing and environmental tobacco smoke exposure are risk factors for severe viral pneumonia in children.
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