Chlamydia pneumoniae has been associated with atherosclerosis and several other chronic diseases, but reports from different laboratories are highly variable and "gold standards" are lacking, which has led to calls for more standardized approaches to diagnostic testing. Using leading researchers in the field, we reviewed the available approaches to serological testing, culture, DNA amplification, and tissue diagnostics to make specific recommendations. With regard to serological testing, only use of microimmunofluorescence is recommended, standardized definitions for "acute infection" and "past exposure" are proposed, and the use of single immunoglobulin (Ig) G titers for determining acute infection and IgA for determining chronic infection are discouraged. Confirmation of a positive culture result requires propagation of the isolate or confirmation by use of polymerase chain reaction (PCR). Four of 18 PCR assays described in published reports met the proposed validation criteria. More consistent use of control antibodies and tissues and improvement in skill at identifying staining artifacts are necessary to avoid false-positive results of immunohistochemical staining. These standards should be applied in future investigations and periodically modified as indicated.

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Background-Recovery of the intracellular bacterium Chlamydia pneumoniae from atherosclerotic plaques has initiated large studies on antimicrobial therapy in coronary artery disease. The basic concept that antibiotic therapy may eliminate and prevent vascular infection was evaluated in vitro and in vivo by examining the antibiotic susceptibility of C pneumoniae in circulating human monocytes, which are thought to transport chlamydiae from the respiratory tract to the vascular wall. Methods and Results-Blood monocytes (CD14ϩ) from 2 healthy volunteers were obtained before and after oral treatment with azithromycin or rifampin and then inoculated with a vascular C pneumoniae strain and continuously cultured in the presence of the respective antibiotic. Progress of infection and chlamydial viability was assessed by immunogoldlabeling and detection of C pneumoniae-specific mRNA transcripts. Circulating monocytes from patients undergoing treatment with experimental azithromycin for coronary artery disease were examined for C pneumoniae infection by cell culture. Antibiotics did not inhibit chlamydial growth within monocytes. Electron microscopy showed development of chlamydial inclusion bodies. Reverse transcription-polymerase chain reaction demonstrated continuous synthesis of chlamydial mRNA for 10 days without lysis of the monocytes. The in vivo presence of viable pathogen not eliminated by azithromycin was shown by cultural recovery of C pneumoniae from the circulating monocytes of 2 patients with coronary artery disease. Key Words: Chlamydia pneumoniae Ⅲ atherosclerosis Ⅲ infection Ⅲ azithromycin Ⅲ rifampin T he obligate intracellular pathogen Chlamydia pneumoniae has been related to atherosclerosis by seroepidemiology, detection of chlamydial structures and, most recently, recovery of viable chlamydiae from atherosclerotic plaques. 1,2 Chlamydiae may thus have a role in the multifactorial pathogenesis of atherosclerosis, a chronic inflammatory condition of the vascular wall. 3,4 On the basis of these findings, antimicrobial treatment studies are currently underway, with the intention to improve the clinical condition of patients with coronary artery disease (CAD) by chlamydial eradication from atheromatous plaques. 5 Endothelial and smooth muscle cells can acquire a productive chlamydial infection that can be inhibited in vitro by common antichlamydial antibiotics. 6 However, chlamydiae are notorious for causing chronic infections, 7 and treatment failure is common. These infections and failures may be due to the establishment of a nonreplicating but viable state of chlamydiae in the host cells. 8 Systemic dissemination of C pneumoniae from the respiratory tract to the cells of the vascular wall requires a cellular transport system, because chlamydiae replicate exclusively within their host cells. The elementary body, the metabolically inactive extracellular life stage of chlamydiae, has never been found circulating free within the bloodstream. Circulating monocytes, which are pivotal to the development of ather...