This interesting study sought to evaluate the effect altitude has on hospitalizations for RSV infection. A multivariate analysis was obtained and suggests that the rate of hospitalization for RSV increased by 25% among infants who were younger than one year of age for every 1,000 meters of altitude. The risk of RSV-associated hospitalization was highest at elevations above 2,500 meters.—SW
Dilemmas for Wheezing Peds
By Chris Miller, MD
Oymar K, Halvorsen T, Aksnes L. Mast cell activation and leukotriene secretion in wheezing infants. Relation to respiratory syncytial virus and outcome. Pediatr Allergy Immunol. 2006 Feb;17(1):37-42.
The wheezing infant is a common problem in pediatric medicine; however, the long-term outcome and risk for recurrent wheezing remains unclear. The authors of this study assert that the risk for recurrent wheezing may be related to the type of inflammation and specific underlying virus during the initial wheezing episode.
Several studies have evaluated the specific contribution of eosinophils to respiratory inflammation in the wheezing child. These studies have found that eosinophilic inflammation may play a role in the airway hyper-reactivity in a child with persistent wheezing. Conversely, little information is available regarding mast cell involvement. This prospective study was designed to assess mast cell activation, in relation to respiratory syncytial virus (RSV) infection and persistent wheezing in wheezing infants.
Researchers enrolled 106 wheezing infants who were subsequently admitted to the hospital. None of these infants had a prior history of wheezing. Infants with prior history of atopic disease, lung disease, or signs of bacterial infection were excluded. RSV testing of nasopharyngeal mucous was performed. Sixty-seven (63%) of the wheezing infants had RSV. An additional 23 healthy infants were selected as controls.
To assess the extent of mast cell activation, urinary prostaglandin F2 (U-PGF2) was measured. To assess for leukotriene secretion urinary leukotriene 4 (U-LTE4) was measured. To evaluate for persistence or reoccurrence of wheezing, a 20-month post-hospitalization follow-up was done. One hundred and three (97%) of the previously hospitalized wheezing infants were available for the follow-up.
The authors used the term “persistent wheezing” to describe those children who experienced at least three wheezing episodes including the first hospitalization. These recurrences were identified either by parental report utilizing a standardized questionnaire or physician/hospitalization records. The remaining children were considered “transient wheezers.”
Review of the data regarding U-PGF2, a specific marker for mast cell activation, showed U-PGF2 to be greatest in the RSV positive patients, followed by the RSV negative patients and finally by the control group. U-LTE4, and thus leukotriene involvement, was also found to be significantly elevated in both the RSV positive and negative wheezing infants compared with the controls. No significant difference was found in U-LTE4 between RSV-positive infants and RSV-negative infants. The transient wheezing infant had a higher U-PGF2 than the persistent wheezing infant. Transient wheezers also had a higher U-LTE4 compared with persistent wheezers, although this was not statistically significant.
With univariate regression analysis positive predictive factors for persistent wheezing included increasing age, RSV negative disease, parental atopy, and male gender. Negative predictive factors for persistent wheezing included an elevated U-PGF2 level.
In discussion the authors conclude that mast cell activation and leukotriene secretion is present in a wheezing infant as noted by increased U-PGF2 and U-LTE4 levels, respectively. Higher U-PGF2 levels in RSV-positive patients indicates that mast cell activation may play a bigger part in the inflammatory process of RSV-induced wheezing compared with non-RSV induced wheezing. Leukotrienes appear to be involved in both RSV and non-RSV wheezing infants. Despite these results, mast cell activation and leukotriene secretion do not appear to be associated with persistent wheezing.