1. The paper records the results of a study of the serological types of haemolytic streptococci in scarlet fever, and their clinical and epidemiological relationships, with particular reference to cross-infection.2. Tables are given showing statistical records of scarlet-fever cases which were examined bacteriologically in an infectious diseases hospital over a period of 13 months. In all, 1831 cases were studied, including 471 with complications.3. In 415 cases in which swab cultures were made from the throat and nose on admission, both throat and nasal swabs yielded haemolytic strepto-cocci in 115, and the nasal swab alone in nine cases (2·5 %). The total number of throat swabs giving positive results was 357. In only two cases were different types of haemolytic streptococci found in the throat and nose.4. Only a single type of haemolytic streptococcus was found to be present in a series of twenty-eight early cases in which many colonies of the primary culture were examined serologically.5. More than one type of haemolytic streptococcus was found in the throats of a series of twenty-five individual cases during a period of residence in hospital when swabs were plated at weekly intervals, and many colonies examined from each plate. In only six of the twenty-five cases did the original type persist throughout the period of residence in hospital. A new type appeared to replace the original strain. In one case three types of haemolytic streptococci were present in the throat at a particular time.6. On the day a complication occurred in a scarlet-fever case only a single type of haemolytic streptococcus was found to be present in the throat or discharge. This suggests that the strain responsible for the complication is present before the complication becomes evident.7. Many colonies from the swab cultures of seven patients, who developed complications, were serologically examined. On the day a complication occurred a single type of haemolytic streptococcus was found present in each case.8. The swab cultures of all the patients in a ward were examined daily over a period of 45 days. Of fifty-five patients thirty-seven were infected by two or more types of haemolytic streptococci. Of these the original type persisted for an average of 9 days. Two or three days before a complication appeared the responsible type was present in the throat.9. 455 cases with complications were studied bacteriologically. In thirty-four the complication was due to organisms other than haemolytic strepto-cocci (7·5%). 280 were due to a type of haemolytic streptococcus other than that with which the patient entered the hospital (61·5%), whereas only ninety-two were due to the same type (20·2%). In forty-nine both the original strain of haemolytic streptococcus and that associated with the complication, could not be typed (10·8%). In patients who had been 2 weeks resident in hospital 90% of complications were due to new types of streptococci.10. Tables comparing the types of haemolytic streptococci found on admission and during the first day of a complication are appended. Reference to the types found in cases which did not develop complications is also made.11. The types of haemolytic streptococci and the severity of the scarlet fever produced by each have been correlated in 949 cases without complications.12. Records are included of a further series of observations made on 390 cases of scarlet fever occurring at a later date. The types of haemolytic streptococci present were compared with those of the same period in the previous year. While type 1 was the prevalent form in the earlier enquiry, type 4 was the dominant form in the later.This work has been carried out with the assistance of the Davidson Research Fellowship in Bacteriology and certain grants from the Moray Fund. I am indebted to Dr F. Griffith for having supplied me with his thirty type strains and specific antisera. I wish to thank Prof. T. J. Mackie and Dr A. Joe for their invaluable assistance. I also wish to express my gratitude to Dr C. A. Green for his interest in the work and his guidance in the early stages of the investigation. Mr James Craig, technician in The City Fever Hospital Laboratories, deserves special mention for his technical assistance.
An inquiry into the incidence of cross-infections, complications and return cases in scarlet fever
