California State Hygienic Laboratory, the forerunner of the current MDL or Microbial Diseases Laboratory, was established by legislative act on July 1, 1905. The laboratory came into existence amidst a major public health crisis - the first plague epidemic of San Francisco. The primary laboratory at Berkeley campus of the University of California soon expended into three branch laboratories in Los Angeles, Fresno and Sacramento. Testing of rabies and the production of antiserum also commenced as early as 1908 in the Pasteur Division of MDL. A Division of Epidemiology soon followed in 2011. The State Board of Public Health decided in 1912 to limit the State Laboratory’s direct testing to cities of less than 25, 000 inhabitants, which lead to earlier branch laboratories becoming local public health laboratories. This decision became an act in 1927 and led to the vast expansion of the local public health laboratories. The State Laboratory took upon reference testing in close collaboration with the local laboratories thus, contributing to the foundation of a strong public health infrastructure, which exists to this day in California.
From its inception, the State Hygienic Laboratory provided high quality reference testing for the control of communicable diseases such as diphtheria, typhoid, gonorrhea and tuberculosis. Other major functions included production of antitoxins and antisera, sanitary microbiology, outbreak investigations, research and teaching. By 1945, the State Laboratory was performing approximately 10% of the total 1,297,774 tests reported by the California public health laboratories with major emphasis on complex culture examinations, confirmatory tests, animal inoculations, serological techniques, and food and water analyses. Although some technology has evolved, the scope of reference testing at MDL has remained unchanged for more than hundred years
Currently, MDL is part of the Division of Communicable Disease Control (DCDC), Center for Infectious Diseases (CID), and the California Department of Public Health (CDPH). It is located since 2003 on the Richmond Campus of the CDPH. The laboratory has five sections: Bacterial Diseases; Foodborne and Waterborne Diseases; High Risk Pathogens; Immunodiagnostic, Mycotic and Parasitic Diseases; and Mycobacterial Diseases. Beside reference testing, MDL conducts applied research and teaching of public health microbiologists and post-doctoral fellows. The laboratory has 60 staff members, which include laboratory directors, public health microbiologists, research scientists, technicians and fellows.