High prevalence of Chlamydia pneumoniae infection in an asymptomatic Jordanian population

The bacterium Chlamydia pneumoniae is associated with respiratory diseases and nonrespiratory illnesses like atherosclerosis. This study aims to investigate the seroprevalence of immunoglobulin G (IgG) against C. pneumoniae in an asymptomatic population in Jordan and to analyze the immunity state in relation to age and sex.

Serum samples were collected from 588 apparently healthy individuals aged 2-86 years. Using the microimmunofluorescence (MIF) test, seropositivity was defined as an anti-C. pneumoniae IgG titer ≥1:16. Titers from 1:16 to 1:256 were considered indicative for a past infection, whereas 1:512 was considered diagnostic of an acute infection.

The overall prevalence of C. pneumoniae was 54.9%. The mean seropositivity in males was slightly higher than females. The seroprevalence of infection was relatively low in children aged 2-9 years, and steadily increased to reach a plateau of 66.7% at around 30-39 years of age, which remained stable in later years. Recent infection was indicated in 14.3% of study subjects. The seropositivity was highest in males, and more frequent in adults than in children and teenagers.

A high seroprevalence of C. pneumoniae in the asymptomatic population suggests that infection with this pathogen is common in Jordan. Higher seropositivity in males compared to females was observed. The primary infection is acquired during the first four decades of life, and in older ages high antibody levels are likely maintained by reinfection or persistent infection.