Kim R. Fox

Vibrio cholerae 01 can assume a ‘rugose’ survival form that resists killing by chlorine, yet retains virulence

Vibrio cholerae 01 is able to shift between smooth and rugose colonial morphologies. Cultures of smooth V. cholerae strains were inactivated in less than 20 s at a concentration of 1.0 mg l‐1 free chlorine. In contrast, cultures of rugose variants exposed to this concentration of chlorine showed an initial rapid drop in viable counts, followed by persistence of a protected subpopulation of cells. Viable V. cholerae could still be recovered from rugose cultures even after exposure to 2.0 mg l‐1 free chlorine for 30 min. Preliminary studies suggest that resistance to killing by chlorine was due to formation of cell aggregates enclosed in a gelatinous mucoid material. Rugose strains appeared to be fully virulent, based on their ability to adhere to Caco‐2 cells and elicit fluid accumulation in rabbit ileal loops. Our data suggest that the V. cholerae rugose phenotype represents a fully virulent survival form of the organism that can persist in the presence of free chlorine.

Improving waterborne disease outbreak investigations

This article is a summary of discussions held and recommendations made at a workshop for the investigation of waterborne disease outbreaks in Chapel Hill, North Carolina, December 7‐8, 1998. Suspected waterborne outbreaks in the United States are primarily investigated by state and local public health officials who may infrequently conduct enteric disease outbreak investigations. Thus, it is important that officials have a formal plan to ensure that epidemiological studies are methodologically sound and that effective collaboration occurs among the epidemiologists, scientists, and engineers who will conduct the investigations. Laboratory support to analyze water samples and clinical specimens should be arranged well in advance of when services may be needed. Enhanced surveillance activities can help officials recognize additional outbreaks and initiate investigations in a timely manner. Epidemiologists should pay more attention early in the investigation to study design, questionnaire development, and sources of bias, especially recall bias, that may affect the interpretation of observed associations. Improved investigations can increase our knowledge about important etiological agents, water systems deficiencies, and sources of water contamination so that waterborne outbreaks can be more effectively prevented.

Assessment of relative potential for Legionella species or surrogates inhalation exposure from common water uses

The Legionella species have been identified as important waterborne pathogens in terms of disease morbidity and mortality. Microbial exposure assessment is a tool that can be utilized to assess the potential of Legionella species inhalation exposure from common water uses. The screening-level exposure assessment presented in this paper developed emission factors to model aerosolization, quantitatively assessed inhalation exposures of aerosolized Legionella species or Legionella species surrogates while evaluating two generalized levels of assumed water concentrations, and developed a relative ranking of six common in-home uses of water for potential Legionella species inhalation exposure. Considerable variability in the calculated exposure dose was identified between the six identified exposure pathways, with the doses differing by over five orders of magnitude in each of the evaluated exposure scenarios. The assessment of exposure pathways that have been epidemiologically associated with legionellosis transmission (ultrasonic and cool mist humidifiers) produced higher estimated inhalation exposure doses than pathways where epidemiological evidence of transmission has been less strong (faucet and shower) or absent (toilets and therapy pool). With consideration of the large uncertainties inherent in the exposure assessment process used, a relative ranking of exposure pathways from highest to lowest exposure doses was produced using culture-based measurement data and the assumption of constant water concentration across exposure pathways. In this ranking, the ultrasonic and cool mist humidifier exposure pathways were estimated to produce the highest exposure doses, followed by the shower and faucet exposure pathways, and then the toilet and therapy pool exposure pathways.

A waterborne Salmonella typhimurium outbreak in Gideon, Missouri: Results from a field investigation

A waterborne disease outbreak associated with Salmonella typhimurium was identified in Gideon, Missouri (population 1104), a town in southeastern Missouri (USA) in December, 1993. It was estimated by the US Centers for Disease Control and Prevention (CDC) that approximately 44% of the city residents developed gastroenteritis during the outbreak. Data from the field investigation was used in a computer program to simulate operations in the water system and to implicate the source of contamination as bird feces in one of the elevated storage tanks.

EPA Drinking Water Security Research Program

The US Environmental Protection Agency (EPA) is the lead US Sector Specific Agency responsible for water security. Research conducted by EPA’s National Homeland Security Research Center (NHSRC) supports the Agency’s Goal 2 “Clean and Safe Water – Ensuring drinking water is safe” and its mission of providing drinking water treatment plants with tools and methodologies to improve water security and recover as quickly as possible should a chemical, biological, or radiological event occur. The research also has multiple benefits in optimizing treatment operations and improving water quality. This chapter is an overview of the NHSRC water security research program and describes research conducted in the areas of prevention, detection/identification, containment, treatment, and decontamination.