Comparison of individuals with and without specific IgA antibodies to Chlamydia pneumoniae: respiratory morbidity and the metabolic syndrome. 
To determine whether a correlation exists between markers for persistent Chlamydia pneumoniae infection, respiratory morbidity, and the metabolic syndrome.  Case-control study.  A group of individuals with serologic markers (specific IgA > or = 1/128) suggestive of persistent C pneumoniae infection were compared with a group of control subjects without IgA antibodies (< 1/32).  Apoteksgårdens Health Care Center, Kopparberg, Sweden.  One hundred case subjects (61 men and 39 women) and 100 control subjects matched for age and gender (mean age, 55 years).  Individuals completed a questionnaire on respiratory symptoms and smoking habits.  Body mass index (BMI) was calculated, BP, and peak expiratory flow (PEF) were determined.  Blood specimens were drawn for determination of high-sensitivity C-reactive protein (hsCRP), blood glucose level, serum lipids, and Chlamydia antibodies.  No significant difference was found between case subjects and control subjects regarding myocardial infarctions, stroke, diabetes type II, BP, BMI, hsCRP, blood glucose levels, and serum lipids.  Symptoms of both asthma and chronic bronchitis were more common in case subjects, as were symptoms of chronic upper respiratory tract infections (p < 0.005).  Case subjects with asthma or chronic bronchitis had more chronic upper respiratory tract disorders (p < 0.05).  Symptoms of chronic respiratory tract diseases increased parallel to increasing specific C pneumoniae IgA antibody titers (p < 0.0005).  PEF percentage of the predictive value was inversely correlated (p < 0.0005) to IgA antibody titers.  The data show that persistent increased levels of C pneumoniae IgA antibodies were associated with pronounced respiratory dysfunction.  These data provide additional evidence suggesting that IgA antibodies may be a marker for persistent C pneumoniae infection.