TYPHOID CARRIERS 369 



and even in the blood of healthy individuals who have merely been in 

 contact with typhoid cases or typhoid carriers, and who show no 

 symptoms of the disease. 



There is evidence that certain individuals are relatively 

 insusceptible to typhoid fever. The cases of the occurrence 

 of typhoid bacilli in the healthy intestine support this view, and 

 it has been further shown that during an epidemic certain 

 persons may suffer from slight intestinal symptoms with typhoid 

 bacilli in the faeces without the disease going through its usual 

 course. The so-called " ambulatory " cases of typhoid fever 

 form a link between these mild infections and fully developed 

 typhoid fever. 



The Epidemiology of Typhoid Fever. Generally speaking, 

 the former prevalence of typhoid fever and the periodic outbreaks 

 which still occur even in well-regulated communities, have de- 

 pended on the capacity of the typhoid bacillus to live and it 

 may be to multiply outside the human body. The investigation 

 of the prevalence of the typhoid bacillus under such saprophytic 

 conditions is a matter of great difficulty, as, for its proper study, 

 the capacity of the organism to multiply when other intestinal 

 and putrefactive organisms are present constitutes the essential 

 problem. Enough is known, however, to show that the bacillus 

 can remain viable under such circumstances for some days, and 

 it may be w r eeks. This fact explains the occurrence of the 

 epidemics due to water, and sometimes, it may be, to milk 

 supplies becoming contaminated with the excreta from typhoid 

 patients. Where surface wells are used, and where sewage, 

 instead of being properly disposed of, finds its way into ash-heaps 

 or cesspools, the way is opened up for communities becoming 

 infected with typhoid fever. 



Typhoid Carriers. In the great majority of cases of typhoid 

 fever, the bacilli disappear from the faeces within from two to 

 ten weeks of convalescence, but in a certain proportion of cases, 

 probably about 2 to 4 per cent., evidence is found of the 

 persistence of the bacilli for many months, and in certain cases 

 their existence has been ileiiioii-tratrd even thirty and, it may be, 

 fifty years after the attack of illness. Persons in whom this 

 phenomenon is present are a constant danger to those around 

 them, as the infectivity of the bacilli frequently remains, and 

 during recent years the importance of such " chronic " carriers 

 has been recognised as explaining many outbreaks of the disease. 

 The cases traceable to such an origin are of the type usually 

 < -lav-Til a- sporadic. They arise amongst persons associated with 

 carrier-, r-;|eeially when the latter are concerned in the prepara- 

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