BackgroundAcute exacerbations of chronic rhinosinusitis (AECRS) are thought to arise from common viral infections progressing to secondary bacterial infections. However, the pathophysiology of AECRS remains poorly understood due to a lack of prospective longitudinal studies.MethodsWe conducted a one‐year prospective longitudinal study involving chronic rhinosinusitis (CRS) adults. At baseline, we assessed subjective symptom scores using a validated upper respiratory infection questionnaire (WURSS), sinonasal outcome testing scores (SNOT‐22), and endoscopic scores (modified Lund‐Kennedy score). Every 2 weeks, we contacted subjects to collect WURSS and SNOT‐22 scores. If WURSS scores were ≥1 and SNOT‐22 scores were ≥ 8.9 compared with baseline, subjects underwent an AECRS assessment. We identified rhinovirus (RV) incidence through viral nasal brushings at each visit and bacterial infection through bacterial swabs if mucus scores were ≥1.ResultsThiry‐five of 80 CRS subjects reported at least one AECRS episode during the year, predominantly occurring in the fall and winter seasons. RV infections were detected in 8 of 35 cases, bacterial infections in 17 of 35, and co‐occurring infections in 7 of 35. All subjects with AECRS visits exhibited significantly higher endoscopic scores compared with baseline. Subjects with co‐occurring RV and bacterial infections demonstrated higher disease severity compared with those with either RV or bacterial infection, or no infection.ConclusionsIn a one‐year prospective longitudinal study involving CRS adults, we identified significant risk factors for AECRS including seasonality and the presence of RV and bacterial infections. These data suggest a standard definition of AECRS and the need to target RV and bacterial infections if we are to help reduce disease severity.