Of particular importance with respect to typhoid was the initiation of research to find a bacterial indicator of the quality and safety of shellfish growing waters. The last case of shellfish-vectored typhoid fever in the United States was reported in 1954. Classification status is based on sanitary surveys of water quality and shoreline surveys of pollution sources. All identified growing waters must be classified as prohibited unless sanitary surveys indicate that water quality meets specific NSSP standards for the other categories. The NSSP standards are rigorous.
Harvesting is permissible in approved areas year-round.
Harvests from waters in these categories typically require substantial state resources for issuing permits, monitoring water quality, creating a management plan, and supervising harvest and transportation. Unfortunately, some potentially productive growing areas remain prohibited for harvest because of inadequate state resources to conduct the requisite sanitary surveys. The primary basis for harvest restrictions is the concentration of fecal coliform bacteria associated with human sewage and with organic wastes from livestock and wildlife. Although chlorine is generally affective in inactivating most bacterial species, including bacterial pathogens, it is less effective against enteric viral pathogens found in sewage, such as the common Norwalk-type virus associated with minor intestinal distress and related problems. The National Shellfish Register provides a record of the acreage of all classified shellfish growing waters in the contiguous United States.