F2 and chronic obstructive pulmonary disease: In a case–control study comparing seroprevalence of B. pertussis in 90 patients with COPD and 90 age- and sex-matched controls with other lung diseases who attended a tertiary care hospital in Hamedan, Iran, a statistically significant association was found between COPD and anti-pertussis toxin (PT) immunoglobulin (Ig) G seropositivity, noting that the presence of IgG antibodies in study participants is indicative of past infection(s).