Foreword 



Legionnaires' disease and its causative agent are subjects of worldwide 

 concern. Tin's is evident from tfie response to an iiiness wliose cause 

 could not initially be defined and from the efforts of the clinical, medical, 

 and general health surveillance communities around the world to treat 

 patients with Legionnaires' disease effectively in order to minimize the 

 threat posed to the public health. 



The staff at the Center for Disease Control (CDC) responded quickly 

 and continues to respond to the need for more complete information on 

 Legionnaires' disease, the bacterium which causes it, methods for confirm- 

 ing a presumptive diagnosis, and the most appropriate therapy. 



The Legionnaires' disease bacterium is special-it does not follow the 

 usual rules. It is a bacterium but remains invisible with traditional bacteri- 

 ological techniques; it does not grow on the usual bacterial media, and it 

 does not stain with the usual bacterial stains. It grows both inside and out- 

 side cells; it mimics some of the laboratory characteristics of rickettsiae, and 

 the clinical characteristics of viruses. This organism does not even seem to 

 follow the usual rules in causing illness; it causes pneumonia under some 

 conditions but not under others, and when it does cause pneumonia, it may 

 mimic viral pneumonia but at the same time leave a few small tantalizing 

 bacterial clues such as an increase in the white blood count. 



We had not identified an important new human bacterial pathogen since 

 the I950's, but now we must ask how many others there might be that do 

 not follow the rules-a real challenge to all microbiologists and clinicians to 

 reevaluate techniques. 



This manual is an effort to disseminate knowledge gained at CDC in the 

 hope that it will be used by the health community for rapid identification 

 of the bacterium and prompt treatment as well as prevention of the illness. 

 It is also hoped that others in academic and research settings will build on 

 the information presented here to further improve diagnostic tools. 



William H. Foege, M. D. 

 Director, Center for Disease Control 



