It is somewhat difficult to determine the length of the incubation period—the time intervening between the occurrence of the infection and the appearance of the first or initial symptom. Its variability is characteristic of scarlet fever. Furthermore, even when infection has occurred, the disease itself may not follow.
Paula N., aged 2:1 years, wrongly transferred to a scarlet fever station, did not show any evidence of the disease until the twenty second day.
Only a minimum incubation period of less than twenty-four hours can positively be determined (Trousseau, Sorensen). This can easily be observed in the case of house infections occurring in tracheotomized patients. The average incubation period is from three to five days.
One attack of scarlet fever usually confers life-long immunity, but second attacks have occasionally been observed.
Theresia B. First attack occurred at the age of three years. Typical angina and unquestionable desquamation. Dismissed from the hospital, January 23, 1898. Readmitted with a second attack April 2, 1902. Highest temperature recorded during this attack, 38.8° C., on the second day. Recurrence by lysis. Temperature normal on the tenth day. Desquamation.
The infrequency of such second attacks of scarlet fever is in marked contrast to diphtheria, where such an occurrence is relatively frequent, even within a few months after recovery from the first attack.
The existence of a natural immunity or an inborn resistance to scarlet fever can not be established, but it is true that only a comparatively small number of children exposed to the infection become ill, and adults, only exceptionally. Certain it is, then, that the resistance to infection in the ease of scarlet fever becomes greater with the advance in years. Family predisposition can not be considered in this connection, because, while in sonic instances all the members of one family are stricken simultaneously, in the greater number of cases only one child becomes ill, or many children suffer from other and various diseases.
It is impossible to state whether family predisposition can be con sidered a prominent factor when all members of a family arc similarly affected or whether it is an evidence of the genius epidemicus.
Three children acquired mild scarlet fever. Lymphadenitis and subsequent nephritis were noted at about the eighteenth day (18, 1S, 19) even the course of the nephritis was the same in all three cases; the urine was albumin-free on the thirty-second, thirty-second and thirty-fourth day.
The greatest susceptibility to the disease is noted in the first decade of life, between the ages of three and eight ; during the first .six months of life resistance to scarlet fever is almost absolute. Diphtheria and whooping-cough, on the other hand, may occur during the first few months of life. The resistance of adults is by no means absolute; the infection may gain a foothold, especially when an increased predisposition has been established by a previous pharyngeal trouble, particularly diphtheria.
Dr. v. P. was on duty in the scarlet fever pavilion from December 1, 1901, to February 1, 1902, and did not contract the disease. Toward the end of March he had a mild attack of diphtheria, returning to duty March 27, 1902, with his pharynx still inflamed. April 5, 1902, yellow ish-grav spots were noted at the posterior pharyngeal wall, and on the hard palate anteriorly. On the following day he presented the typical scarlet fever eruption.
I have seen two exactly similar eases in the past two years.
I have already referred to the fact that scarlatinal infection may and does occur at the site of wounds, injuries of various kinds, especially burns (Leiner): in fact, there is noted at such times a peculiar pre disposition to infection. The same is true during the puerperium.
Occasionally the reason for the occurrence of scarlet fever can not. be determined.
For instance, Johanna R. became ill with scarlet. fever after being on duty as nurse in the scarlet fever pavilion only two days.
The relationship of this disease to a diminishing predisposition is vastly different from what occurs in the case of measles, where, irre spective of the age of the individual, infection occurs at the first exposure. The onset of these two diseases in epidemic form in closed institutions is also distinctive. In the case of measles many cases occur at one time and the epidemic outbreak terminates rapidly. In the case of scarlet, fever, on the other hand, the number of cases rises steadily, and sporadic cases occur for a long time afterward.