113 
pied by the secondary case, the number of flies in the neighborhood 
and the readiness with which they could pass from the infected 
excreta of the known case to the food of the persons subsequently 
attacked, and all other conditions thought to have any bearing on 
the situation, were taken into consideration. 
Fom cases gave a history of association with persons convalescent 
from typhoid fever. 
Estimating the chances of these 97 cases having become infected 
by contact at about 50 per cent, and adding 48 cases so deduced to 
the 66 cases considered as almost certainly having been infected by 
contact, there were 114, or about 21 per cent, of the 542 cases attribu- 
table to contact infection. 
These 114 cases comprise about 17 per cent of the total 665 cases 
investigated, as against about 15 per cent (estimated on the same 
basis of probability) of the 670 cases investigated in 1907 and about 
6 per cent of the 866 cases investigated in 1906. 
BACILLUS CARRIERS. 
In consideration of the likelihood of clironic bacillus carriers playing 
a part in the dissemination of t}q)hoid fever in the District of Columbia 
the following data in regard to known association of the 542 cases 
with persons who, within the five j^ears previous, had had typhoid 
fever were obtained : 
Number of cases and amount of associa- 
tion. 
Association 30 days prior with persons who had had typhoid 
fever vithin— 
Intimate. 
Fairlj 
intimate. 
Slight. 
Total 
cases. 
6 months 
1 
1 
2 
4 
6 months to 1 year 
9 
0 
2 
11 
1 to 2 years 
’ 8 , 
4 
3 
15 
2 to 3 years 
' 3 
0 
3 
6 
3 to 4 years 
* 3 
2 
0 
5 
4 to 5 years 
8 
0 
0 
8 
Total 
: 32 
7 
10 
49 
No known association 
I 
493 
Grand total ■ 
i 1 
542 
i . 1 
i 
1 
For people living in a large city there is, of course, much association 
with persons which would be difficult, if not impossible, to trace. 
Therefore the data in the above table presented for the cases studied 
in 1908, like those for the cases studied in 1907, refer almost entirely 
to association with members of the family or with intimate acquaint- 
ances. The number of cases giving a history of such association is, 
therefore, far below the actual. 
179— Bull. 52—09 8 
