Acute exacerbations of chronic rhinosinusitis (AECRS) have a negative effect on health-related quality of life (QOL) and patient productivity independent of baseline chronic rhinosinusitis (CRS) symptoms.1, 2 AECRS are currently defined in consensus guidelines as a transient worsening of symptoms that return to baseline symptoms, often requiring intervention with systemic corticosteroids or antibiotics.3, 4 Because of the inexact nature of this definition of AECRS, many previous research studies have used patient-reported use of systemic antibiotics and corticosteroids for CRS as proxy measures for AECRS.5, 6 In a recent study by our group, which directly investigated patient experiences with AECRS using interviews and qualitative methodology, we proposed an evidence-based and patient-centered definition for AECRS as: “A flare up of symptoms beyond day-to-day variation to which a distinct negative impact on a patient's QOL or functionality can be attributed.”7 However, there remains a need to establish a duration criterion for the increased symptoms that defines the occurrence of an AECRS. Does one hour, day, or week of elevated sinonasal symptoms constitute an AECRS? Is there a minimum length of time that patients need to experience elevated symptoms for episodes that they define as a flare, seek treatment for, or specifically recall as an AECRS at their next CRS-associated visit? As AECRS have been shown to be a major, independent driver of diminished QOL and morbidity in CRS,1, 8 it is clearly important to understand this phenomenon that patients report at their clinic visits. To this end, we performed a qualitative study of patients with CRS to investigate and determine a minimum duration criterion for AECRS that is directly based on patient perceptions of AECRS. This study was approved by the institutional review board of the University of Cincinnati College of Medicine. English-speaking adult patients (18 years and older) with a diagnosis of CRS were recruited. Informed consent was obtained. Exclusion criteria included diagnosis of cystic fibrosis, vasculitis, sarcoidosis, immunodeficiency, and recent surgery. Basic demographic information and clinical characteristics (smoking status, history of nasal polyps, history of endoscopic sinus surgery, comorbid asthma, and allergy confirmed by skin prick or serological test) were obtained and recorded. This was a qualitative phenomenological study using constant comparative methodology. The content of the interview protocol was determined and a standardized script was developed. Twelve one-on-one interviews with participants were conducted. Recruitment ended when content saturation was met. Conversations were recorded and transcribed, removing all patient identifiers. Two of the authors (Z.A.W. and K.M.P.) served as coders and a codebook was created and used to identify recurrent themes. Descriptive statistics were used to summarize the participant demographics and clinical characteristics. The interviews were transcribed and coded. Through iterative discussion among the research team, themes were analyzed for meaning and conclusions were drawn. Patient characteristics are listed in Table 1. A total of 12 patients, with interviews ranging in duration from 3 to 15 min, were ultimately needed to reach content saturation. When directly asked about a minimum duration of increased symptoms to define a “flare up” or AECRS, 47.7% of patients reported 4 to 5 days, 16.7% reported 7 to 10 days, while the remaining 47.7% patients reported 1 to 3 days. Participants cited several reasons why they would contact their physician regarding an AECRS, including duration of symptoms (usually 7 to 10 days), discolored nasal drainage and facial pain, extranasal symptoms (ear issues, pulmonary exacerbation, fatigue, or headache) and impact on productivity. Finally, when asked what the duration of increased symptom severity would have to be present to remember the AECRS 2 weeks later, the majority of participants stated symptoms would have to last for at least a week. Table 2 provides a representative selection of patient answers to interview questions. 24 to 72 hours. Two to 3 days of increased symptoms. Usually within a couple days. It starts off really simple, or you think it's going to be simple. And then all of a sudden it just snowballs downhill from there. And then within 3 days, I'm on the phone with primary care saying “hey, I already know it's brewing again.” By day 3 I'd notice it. Probably 3 days. It might take it like 4 days. [I] may consider it a flare after 4 days or so but then [I] may not seek treatment until closer to 1 week or 10 days. Usually about 5 days. Four or 5 days. So I would say yeah, a good 5 days is about average for me. Something lasting close to a week. Yeah, I would say around a week. Usually I have very thick yellow snot and it starts going into my lungs and I cough and that's usually when I call for a prescription of [Augmentin]. That trigger would be that I get the thick green snot and it becomes a sinus infection and I need to get treatment for it. Usually my primary care physician likes to let it go week before I get antibiotics. [I base it more on] duration of over a week because unfortunately, I think the severity doesn't bother me as much Usually for me, unfortunately, I wait until it gets really bad. I wait until there's more pain, a headache, drainage, a cough. I wait until it's unfortunately a little bit later. I'm like, “Oh, maybe it'll just go away.” Yeah. Yeah. It's really when the symptoms are, I'm like, “I'm not going to get this under control.” Definitely after 10 days, I'm going to be on the Epic app. I feel like when I also kind of get like the aches and the increased fatigue and just the pressure gets worse or it's affecting me more to where like I'm missing work. Probably anything that lasts 48 hours or more. I would say like at least a week, probably. They're always tied to having a cold, so I always remember them because they follow a cold. So, most of the time they last that full 7 to 10 days and so it sticks in your head. I'd say about a week. It is a little bit less related to the duration, but more the severity. I would say typically last about a week. A week or longer, I guess. I remember if it affected my capacity to function. Usually, they last about a week at that point when people start to say stuff, is when I remember them. AECRS are now recognized as a distinct entity that can independently influence QOL.1 However, the working definition of AECRS has historically been broad and variable across the literature. Although we recently proposed a novel evidence-based and patient-centered definition of AECRS,7 the goal of this present study was to establish a minimal duration criterion for elevated symptoms to define an AECRS. Of the patients interviewed, the majority of participants described AECRS as an increase in symptoms lasting 3 to 7 days in duration. Furthermore, a majority of our participants felt that to recall an AECRS after 2 weeks (the same recall period as the 22-item Sino-Nasal Outcome Test [SNOT-22]), the episode would have to last about a week. Interestingly, some participants classified their exacerbations based solely on severity of symptoms, while others did so based on duration of increased symptoms, even if only reflecting a mild increase from baseline. Finally, participants discussed duration of symptoms over a week, discolored nasal drainage, facial pain, extranasal symptoms, and impact on productivity as reasons why they would contact their healthcare provider regarding an AECRS. From this information, we propose adding a minimum of 3 days of elevated symptoms to the working definition of AECRS as this would conservatively capture the majority of the study population's exacerbations. Interestingly, this is consistent with the recommended threshold duration of worsening symptom to start oral corticosteroids for an asthma exacerbation.9 Based on our findings reported here, we suggest a more comprehensive definition of AECRS as “a flare up of symptoms beyond day-to-day variation, lasting at least 3 days, and to which a distinct negative impact on a patient's QOL or functionality can be attributed.” As we become more specific in this definition, we can then go on to study AECRS more reliably in a prospective, quantitative manner.