The prevalence of undiagnosed chronic obstructive pulmonary disease in a primary care population with respiratory tract infections - a case finding study

BACKGROUND: Chronic obstructive pulmonary disease (COPD) is an underdiagnosed cause of morbidity and mortality worldwide. Prevalence of COPD has been shown to be highly associated with positive smoking history and increasing age. Spirometry is the method used for diagnosing COPD. However, identifying patients at risk of COPD to undergo spirometry tests has been challenging. Therefore, there is a need for new cost-effective and feasible diagnostic screening procedures for use in primary care centers. Our aim was to describe the prevalence and severity of undiagnosed COPD in a group of patients with respiratory infections attending urgent primary care, and to identify those variables in patients' history that could be used to detect the disease. METHODS: Patients of 40-75 years (n = 138) attending urgent primary care center with acute respiratory tract infection, positive smoking history and no previously known pulmonary disease underwent pre- and post bronchodilator spirometry testing four to five weeks after the acute infection. Prevalence and severity of COPD were estimated following the Global Initiative for COPD (GOLD) criteria. Variables such as sex, age, current smoking status, smoking intensity (pack years) and type of infection diagnosis were assessed for possible associations with COPD. RESULTS: The prevalence of previously undiagnosed COPD in our study group was 27%, of which 45% were in stage 1 (FEV1 ≥ 80% of predicted), 53% in stage 2 (50 ≤ FEV1 < 80% of predicted), 3% in stage 3 (30 ≤ FEV1 < 50% of predicted) and 0% in stage 4 (FEV1 < 30% of predicted). We found a significant association between COPD and age ≥ 55 (OR = 10.9 [95% CI 3.8-30.1]) and between COPD and smoking intensity (pack years > 20) (OR = 3.2 [95% CI 1.2-8.5]). Sex, current smoking status and type of infection diagnosis were not shown to be significantly associated with COPD. CONCLUSION: A middle-aged or older patient with any type of common respiratory tract infection, positive smoking history and no previously known pulmonary disease has an increased likelihood of having underlying COPD. These patients should be offered spirometry testing for diagnosis of COPD.