not able to cause a new infection. Diseases Chlamydia pneumoniae is a common cause of pneumonia around the world; it is typically acquired by otherwise-healthy people and is a form of community-acquired pneumonia. Its treatment and diagnosis are different from historically recognized causes, such as Streptococcus pneumoniae. Because it does not gram stain well, and because C. pneumoniae bacteria is very different from the many other bacteria causing pneumonia (in the earlier days, it was even thought to be a virus), the pneumonia caused by C. pneumoniae is categorized as an "atypical pneumonia". One meta-analysis of serological data comparing prior C. pneumoniae infection in patients with and without lung cancer found results suggesting prior infection was associated with an increased risk of developing lung cancer. In research into the association between C. pneumoniae infection and atherosclerosis and coronary artery disease, serological testing, direct pathologic analysis of plaques, and in vitro testing suggest infection with C. pneumoniae is a significant risk factor for development of atherosclerotic plaques and atherosclerosis. C. pneumoniae infection increases adherence of macrophages to endothelial cells in vitro and aortas ex vivo. However, most current research and data are insufficient and do not define how often C. pneumoniae is found in atherosclerotic or normal vascular tissue. Chlamydia pneumoniae has also been found in the cerebrospinal fluid of patients diagnosed with multiple sclerosis. Chlamydia pneumoniae infection was first associated with wheezing, asthmatic bronchitis, and adult-onset asthma in 1991. Subsequent studies of bronchoalveolar lavage fluid from pediatric patients with asthma and also other severe chronic respiratory illnesses have demonstrated that over 50 percent had evidence of C. pneumoniae by direct organism identification. C. pneumoniae infection triggers acute wheezing, if it becomes chronic then it is diagnosed as asthma. These observations suggest that acute C. pneumoniae infection is capable of causing protean manifestations of chronic respiratory illness which lead to asthma. Macrolide antibiotic treatment can improve asthma in a subgroup of patients that remains to be clearly defined. Macrolide benefits were first suggested in two observational trials and two randomized controlled trials of azithromycin treatment for asthma. One of these RCTs and another macrolide trial suggest that the treatment effect may be greatest in patients with severe, refractory asthma. These clinical results correlate with epidemiological evidence that C. pneumoniae is positively associated with asthma severity and laboratory evidence that C. pneumoniae infection creates steroid-resistance. A meta analysis of 12 RCTs of