Nasal Colonization with Staphylococcus Aureus Before Radiation Therapy Predicts Radiation Dermatitis: A Prospective Study

Acute radiation dermatitis (RD) is a common side effect of radiation therapy (RT). Radiation-induced skin changes are thought to increase the risk of secondary skin infection. However, little is known regarding the baseline incidence of microbial colonization prior to RT and whether it is associated with development of RD. The goals of our prospective study are to 1) characterize the incidence of baseline bacterial colonization in patients undergoing RT, and 2) examine the association between radiation dermatitis severity and baseline bacterial colonization. We hypothesize that microbial colonization prior to initiation of RT is associated with development of RD. We are presenting preliminary results from a prospective trial in which patients with cancers of the head and neck, breast, or anus undergo bacterial culture from the nares and the area of skin subject to radiation, prior to RT initiation. Patients are evaluated weekly during RT, and dermatitis is graded using CTCAE version 4.0. Descriptive statistics and odds ratios are utilized to present associations between culture results and skin toxicity. Forty-eight subjects with cancers of the breast (48%), head and neck (44%), and anus (8%) have completed RT to date. Baseline bacterial culture for Staphylococcus aureus was positive in the nares for 10 subjects (21%) and positive on the skin in 3 subjects (6%). All 3 subjects with positive skin cultures also had a positive nares culture. Twenty-eight patients (58%) developed grade 1 dermatitis, 15 (31%) developed grade 2 dermatitis, and 5 (10%) developed grade 3 dermatitis. 18 subjects (38%) received silver sulfadiazine for RD. Positive culture for S. aureus at baseline was associated with increased risk of grade 2-3 dermatitis (80% v. 32%, OR=8.7, p=0.012) and with receipt of silver sulfadiazine (70% v. 29%, OR=5.7, p=0.025). Bacterial colonization with S. aureus prior to RT initiation is a risk factor for developing high-grade RD. Because a positive nares culture was able to predict skin toxicity, even in the absence of a positive skin culture, antimicrobial therapy in the nares prior to RT initiation ought to be explored as a strategy to lessen the severity of RD. Further studies are needed to understand the association between microbial colonization and development of RD.