Among 926 adult patients who consulted a general practitioner unit with prolonged coughing, we examined the clinical features of the 52 who showed high-level PT-IgG antibody titer results indicating pertussis. Paroxysmal coughing was observed in 31 cases (59.6%), whooping cough was observed in 9 cases (17.3%), and 15 cases (28.8%) of posttussive vomiting were observed. However, no characteristic pertussis symptoms were observed in 15 cases (28.8%). Explaining the diagnosis via the high levels of the antibody titer significantly reduced anxiety in the patients, who had already consulted a number of medical institutions. Bronchodilator was effective in half the cases, but no correlation with FeNO was observed; accordingly, it was thought that there had been a spontaneous remission of coughing. It is important to consider a diagnosis of pertussis in patients suffering cough-variant asthma due to prolonged coughing.