EPIDEMIOLOGY. 
In the study of the prevalence of typhoid fever in the District of 
Columbia we investigated all cases reported to the health office dur- 
ing the period from June 1 to November 1, 1906, a total of 868 cases. 
It was not practicable for us to study the cases in clinical detail and 
generally the diagnosis as made b}^ the attending physician was 
accepted; however, the histories of two cases pointed so strongly 
against their being typhoid fever that they were eliminated, leaving 
866 cases for consideration in this report. 
At the beginning of our studies of t}^phoid fever the correct diag- 
nosis of cases was appreciated to be of first importance. With this 
in view the following circular letter was addressed to all the physi- 
cians in the District of Columbia. 
Public Health and Marixe-Hospital Service, 
Hygienic Laboratory, 
Washington, July 14, 1906. 
My Dear Doctor: In view of the prevalence of typhoid fever in the District of 
Columbia, the United States Public Health and Marine-Hospital Service, with the 
cooperation of the health department of the District of Columbia, has undertaken an 
investigation of the origin and prevalence of this disease. The undersigned board of 
officers of the Service has been appointed by the Surgeon-General, with the approval 
of the Secretary of the Treasury, to conduct this investigation. 
It is our desire to make the investigation as thorough and comprehensive in its scope 
as the means at our disposal and circumstances will permit, and we hope to secure your 
active aid and cooperation. 
We shall be glad to make Widal tests, blood cultures, and Diazo tests in any cases 
that you desire. We are also authorized to make, for registered physicians, bacterio- 
logical and chemical examinations of water, milk, and other possible sources of typhoid 
infection. 
All of these tests and examinations will be made free of cost at the Hygienic Labora- 
tory, Twenty-fifth and E streets NW, 
Very respectfully, M. J. Rosenau, 
Director Hygienic Laboratory . 
J. H. Kastle, 
Chief, Division of Chemistry. 
L. L. Lumsden, 
Passed Assistant Surgeon. 
This letter met with a cordial response and had the twofold effect 
of bringing us in closer touch with the situation and of aiding in the 
diagnosis of doubtful cases. 
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