Author ’ s response to reviews Title : Air pollution exposure is associated with MRSA acquisition in young U . S . children with cystic fibrosis Authors :

the term “other” respiratory pathogen/infection may be a typo (page 2, lines 17 and 41) We have revised the Background section of the Abstract and it now reads, “We recently demonstrated that chronic PM2.5 exposure is associated with an increased risk of initial Pseudomonas aeruginosa acquisition in young children with CF. The purpose of this study was to determine whether PM2.5 exposure is a risk factor for acquisition of other respiratory pathogens in young children with CF.” “initial” (line 17) should be placed closer to “acquisition” (line 21). We have revised the sentence in the Methods section of the Abstract so that “initial” and “acquisition” are closer together; it now reads “We conducted a retrospective study of initial acquisition of methicillin susceptible and methicillin resistant Staphylococcus aureus (MSSA and MRSA), Stenotrophomonas maltophilia and Achromobacter xylosoxidans in U.S. children <6 years of age with CF using the CF Foundation Patient Registry, 2003-2009.”