Leptospira agglutination tests of 29,317 human sera submitted to the Iowa State Hygienic Laboratory for brucella serology during 1958–1959 revealed 0.5 percent positive for leptospirosis at titers of 1:20 or higher. Field investigation of suspect acute and recent cases resulted in confirmation of 82 leptospiral infections. A total of 42 sporadic infections was identified among live-stock farmers, packing-plant workers and veterinarians; a local epidemic of 40 cases was confirmed among individuals exposed to contaminated streams. Serologic surveillance of patients revealed initial heterologous serotype response in many instances; however, the homologous serotype immune reaction eventually predominated and persisted. Leptospira pomona was incriminated as the infecting leptospira serotype in all but two cases; one patient was infected with L. icterohaemorrhagiae following contamination of lacerations with mud polluted with rat dejecta, and one case defied specific serotype definition. L. pomona was isolated from the urine of 2 of 52 human cases and 5 of 88 bovine contacts.
Laboratory procedures, field investigational methods and clinical characteristics are described. Factors which may be responsible for the under-recognition of human leptospirosis are suggested.
Formerly Assistant Professor, Department of Preventive Medicine and Hygiene (Institute of Agriculture Medicine), College of Medicine, State University of Iowa; presently Chief, Epizootiology Section, National Cancer Institute, U. S. Public Health Service, Bethesda, Maryland.
Chief, Veterinary Public Health Laboratory, Communicable Disease Center, U. S. Public Health Service, Atlanta, Georgia.