In the laboratory tests the prime reliance must be placed in blood culture, which of course should be made during the first ten days of the illness. Blood cultures give positive results in the inoculated as well as in those not protected by vaccination.
Agglutination tests are the ones of choice after such a period, but one must discount agglutination in those who have been vaccinated previously. Of course the rising agglutination titre during the course of the disease gives valuable information, and the Dreyer technique, where simultaneous tests are made on emulsions of typhoid, paratyphoid A and paratyphoid B at intervals of 4 days, noting a distinct rise for one of these organisms, is based on this factor. At the same time this technique is exacting and does not seem to have given the results that were at first expected.
Culturing the urine is of more value in diagnosis than that of the faeces. Bacilluria may be expected in about one-fifth of cases after the second week. Faeces culturing gives positive results in a smaller proportion of cases and is attended with much difficulty.
The Paratyphoid Fevers.—The paratyphoids would seem to be more prevalent, in proportion to typhoid, in the tropics than in temperate climates, thus in India, of 1886 British soldiers, convalescent from enteric fevers, 791 were diagnosed as typhoid, 633 as paratyphoid A, 136 as paratyphoid B and 326 as enteric cases of uncertain etiology. Paratyphoid B cases seem more frequent in temperate climates than paratyphoid A ones, as noted during the war in France. Cruickshank, and Lafrenais, in a study of carriers, among the 1886 cases noted above observed that 49 became carriers and of these 34 were from paratyphoid A cases, 9 from typhoid convalescents and 6 from paratyphoid B convalescents. Of 13 chronic carriers (those carriers excreting organisms after a period of six months) 8 were carriers of paratyphoid A, 4 of typhoid and 1 of paratyphoid B.
This evidence would indicate that paratyphoid A, once introduced, would spread more widely than the other enteric affections.
Clinically, paratyphoid A cases resemble typhoid ones rather closely, although as a rule less severe in course. With paratyphoid B the course is less severe than with the other enteric organisms but it often shows an abrupt onset and is frequently similar to cases of meat poisoning. This organism and the Gärtner bacillus are common excitants of the so-called ptomaine poisoning cases. Paratyphoid B cases show a tendency to localize in the pelvis of the kidney or elsewhere and may cause a broncho-pneumonia.
Colon Infections.—Such infections seem to be rare in temperate climates other than as localized conditions especially of the urinary bladder. Cholecystitis is not infrequently due to a colon bacillus infection. In the tropics, however, especially following bacillary dysentery, we may have a generalized infection which may result in a fatal septicaemia. In such cases abscess formation in the kidneys is usually found.
Cases diagnosed as mild typhoid fever have as a result of blood cultures been found to occasionally be due to a colon bacteriaemia.
In temperate climates as well as in the tropics pyelitis is often due to a colon infection and probably 10% of cases of appendicitis are caused by the colon bacillus alone, although it is extremely frequent in association with streptococci or staphylococci.
Bacillus alkaligines faecalis infections. Cases similar to typhoid fever have been found to be due to infections with this member of the typhoid-colon group of organisms.