<prompt> Reactive cold agglutinins suggests which one of the following diseases?Chronic infectious mononucleosisPrimary syphilisScarlet feverPrimary atypical pneumonia  <response>: Mycoplasma pneumoniae causes primary atypical pneumonia. Although physicians rely on the presence of cold agglutinins CA for diagnosis, CA may be negative in up to 50 of cases. With symptoms of pneumonia, a positive CA is reliable. A complement-fixation CF test for M. pneumoniae is indicated when CA is negative. Isolation of M. pneumoniae is time-consuming 1 to 3 weeks and not practical in most circumstances. 