[Detection of serum Chlamydia pneumoniae antibodies and analysis of epidemiologic data in 5 years]

To detect serum Chlamydia pneumoniae (C.pneumonia) antibodies and analyze the epidemiologic data.

Micro-immunofluorescence (MIF) was used to detect IgG and IgM antibodies against C.pneumoniae in 7 802 serum specimens from May 2008 to September 2013. C.pneumoniae past or recent infections were determined based on specific IgG and IgM antibodies and their titers. The analysis of relationship between age, gender and other clinical factors associated with antibody titers was performed.

The positive rate of C.pneumonia IgG antibodies ( ≥ 1: 16 and <1: 512) was 87.5% (6 827/7 802). And the lowest rate of 50.6% (78/154) was shown in patients of 2-4 years age group while the highest rate of 98.7% (1 277/1 294) in those above 70 years old. The average geometric mean titer (GMT) of C.pneumonia IgG antibodies was 43.9. GMT in males was significantly higher than that in females (45.8 vs 41.9, P = 0.000 1). And 282 (3.6%) patients were diagnosed with recent C.pneumoniae infection (IgG ≥ 1: 512 or IgM ≥ 1: 16 or acute and convalescent serum antibody titers turned to positive or four times and more elevated). The lowest rate of 0.5% (2/417) was detected in < 2-year-old patients while the highest rate of 6.7% (24/357) in 10-14-year-old group patients. The miss ratio was as high as 68.1% (192/282) if C.pneumoniae IgM antibody was used as an only criteria for C. pneumoniae recent infection. The recent infection rates in patients with autoimmune diseases (7.1% (24/336) ) and those with pneumonia/chest radiological shadow findings (4.7% (69/1 467)) were statistically higher than the average rate (3.6%) of total population (P = 0.000 4, 0.014 0).

The positive rate of C.pneumonia IgG antibody is quite high in the population. And the GMT of C.pneumoniae IgG antibody in males is significantly high than that in females. Recent C.pneumonia infection is to be missed if IgM antibody is used as a sole criterion.