rs12252 was not associated with susceptibility to influenza-related critical illness in children or with critical illness severity. Our data also do not support it being a splice site.

IMPORTANCE Despite a high disease burden, there is no effective treatment for respiratory syncytial virus (RSV) infection. OBJECTIVES To determine whether administration of azithromycin (AZM) to children with RSV-induced respiratory failure is safe and to define the effect of AZM therapy on nasal matrix metalloproteinase 9 (MMP-9) levels. DESIGN, SETTING, AND PARTICIPANTS This randomized, double-blind, placebo-controlled phase 2 trial was conducted at a single tertiary pediatric intensive care unit from February 2016 to February 2019. The study included children with RSV infection who were admitted to the pediatric intensive care unit and required respiratory support via positive pressure ventilation (invasive and noninvasive). A total of 147 children were screened; 90 were excluded for not meeting inclusion criteria, having an absent legal guardian, lacking pharmacy support, or having a language barrier and 9 declined participation, resulting in 48 patients enrolled in the study. INTERVENTION Receipt of standard dose AZM (10 mg/kg/d), high-dose AZM (20 mg/kg/d), or a matching placebo of normal saline intravenously for 3 days. MAIN OUTCOMES AND MEASURES Nasal and endotracheal samples were collected at baseline as well as at 24 hours and 48 hours after start of treatment. The secondary outcome was to determine treatment effect on clinical outcome measures, including days of positive pressure ventilation and length of hospital stay. RESULTS A total of 48 patients were enrolled in the trial, with a median (range) age at randomization of 12 (1 to 125) months; 36 participants (75.0%) were younger than 2 years. Overall, 26 participants (54.2%) were boys, and 29 (60.4%) had a comorbidity. A total of 16 patients were randomized into each trial group (ie, placebo, standard-dose AZM, and high-dose AZM). Baseline demographic characteristics were comparable among the 3 groups. Both doses of AZM were safe, with no adverse events observed. No difference in nasal MMP-9 levels were observed between treatment groups. Among those who required mechanical ventilation and received high-dose AZM, endotracheal active and total MMP-9 levels were lower on day 3. Compared with baseline, active and total MMP-9 levels in endotracheal aspirates were 1.0 log lower in the high-dose AZM group (active

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