Reactive cold agglutinins suggests which one of the following diseases?

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.