Using a large academic institutional EHR collected for 8 years, this study described the clinical characteristics and healthcare utilization of newly referred patients with subacute and chronic cough to the tertiary allergy and asthma clinics in Seoul, Korea. Cough was a common chief complaint, comprising a large proportion of all referrals to the clinics (46.7% of 28,312 referrals). In patients with either subacute or chronic cough, cough was frequently accompanied by anterior nasal (about 50%), lower airway (30%), or acid reflux symptoms (20%), and also by test abnormalities in chest X-rays, spirometry, or T2 inflammation markers, indicating the heterogeneity of clinical presentation of subacute and chronic cough patients visiting allergy and asthma clinics.
It has been conceived that cough is one of the most common reasons why patients seek medical care . However, comprehensive large-scale data is scarce. In the US National Ambulatory Medical Care Survey, acute cough was a common reason for seeking outpatient consultation . In the Asia-Pacific multicenter questionnaire survey of 5,250 allergic or respiratory patients, cough or coughing up phlegm was frequently reported as the main reason for the outpatient visit (23%) . However, the Asia-Pacific study  focused only on patients with an established diagnosis of allergic rhinitis, rhinosinusitis, asthma, or COPD. Both surveys [13, 12] lacked specific information on cough characteristics and cough-related healthcare utilization. In this regard, our findings are a valuable addition to the literature, providing specific data on cough presentation and subsequent healthcare utilization in the real world.
Recent real-world studies from the US reported the disease burden in patients with chronic cough (vs. those without chronic cough), including increased healthcare resource utilization, outpatient visits, diagnostic tests, and treatment needs [14–16]. Our findings are generally in line with these [14–16]. We found a substantial proportion of patients who required additional diagnostic tests, drug treatments, and outpatient visits, among the new referrals. Codeine-containing drugs were given to 21.5% of patients with chronic cough, and oral antibiotics to 23.7% and OCS to 9.9%; these drugs have potential concerns with overuse, side effects, complications, or antimicrobial resistance in the long term[11, 10]. Given their potential health risks, the medication uses and health consequences should be the outcomes of long-term follow-up studies of cough patients.
It should be noted that subacute cough was the chief complaint in 34.8% of this tertiary care population, which was much higher than expected. This high proportion is likely attributed to the national healthcare systems in South Korea, which allow easy and rapid access to tertiary care hospitals even with a simple referral letter from a primary clinic , and the findings are presumably distinct from some countries with strict referral systems like the UK. Although lower than those with chronic cough, the proportion of subacute cough patients who required additional diagnostic tests (e.g., chest CT in 21.6%) and drug treatments (codeine-containing drugs in 18.3%, and OCS in 6.6%) was considerable. These findings suggest large unmet clinical needs in patients with subacute cough as well.
Compared to previous small studies of Korean patients visiting specialist cough clinics [18, 19] or a recent clinical trial participant with refractory chronic cough , our study population were relatively younger (mean age 52.9 years) and less women (63.6%) and had shorter cough duration (median 6 months). A major reason for the differences, we suppose, is that the latter was derived from allergy and asthma clinics, while the formers were from specialist cough clinics. In this regard, the information presented here may represent the characteristics of chronic cough patients at more general allergist and pulmonologist clinics.
This study had several limitations. First, it is a tertiary institution-based analysis, and thus has limited external validity. Second, there is a risk of misclassification as the information on cough characteristics and history relied on patient reports collected during routine clinical practice. Also, cough-associated symptoms were recorded in a dichotomous manner. Third, tools to evaluate cough severity or impact on life were not included in the routine EHR data collection. Their inclusion would help to increase the utility of institutional RCD analyses. Fourth, our study did not evaluate unstructured, free-text data at follow up visits, and thus could not evaluate treatment responses. Finally, as our analyses were limited to an academic institutional EHR database, healthcare utilization outside the institution could not be evaluated. However, most limitations are intrinsic to the nature of institutional RCD analysis; and it has strengths in large sample size and detailed longitudinal data collection including cough-related prescriptions, diagnostic tests, and healthcare utilization.
In conclusion, cough was a common chief complaint among new referrals to tertiary allergy and asthma clinics. Patients with either subacute or chronic cough had frequent comorbidities and different accompanying symptoms, indicating the heterogeneity of clinical presentations. They frequently required additional diagnostic tests, drug treatments (including OCS and codeine), and outpatient visits, suggesting the disease burden and future health risk. Further studies are needed to understand long-term health outcomes and reduce the disease burden of cough.