Tuesday, March 7, 2017

The Importance of Backflow Prevention

Questions often arise on the need for backflow prevention devices on water spigots in food establishments. Backflow occurs when non-potable water is pulled into the potable water via a cross-connection - is a physical link between potable and non-potable water, such as a hose.  Backflow occurs when there is a high movement of water through a water main, which generates negative pressure in the cross connection, causing back-siphonage or backflow from the non-potable water source through the cross-connection, whether that be a hose or a pipe.  This is due to Bernoulli's principle.

Examples of cross connections can be someone dropping a hose connected to a sink into a mop bucket containing floor cleaner, or someone dropping an outside hose into a non-chlorinated swimming pool (green) or into puddle of water.  Hoses, however, are not the only issue.  An often overlooked connection is the direct water feed into chemical mixing systems.   Hazards related to backflow are not always biological.  Chemicals can be pulled into the water source, especially through this direct water feed into chemical mixing / dispensing systems.

Of course it is best not to make that cross connection, but this is not always easy when using hoses.  Where hoses are used, it is important to make sure back flow prevention devices are installed.
Pressure deficiencies, such as when there is a water main break, also can result in backflow into the potable water source.
From a study looking at water related outbreak, CDC stated
 "Cross-connections and backsiphonage represented the largest underlying contributing factors among distribution system deficiencies identified in drinking water outbreaks reported during 1971–2006 (6), indicating that greater attention should be focused on cross-connection and backflow prevention and on maintaining the integrity of the distribution system. Drinking water quality within the distribution systems of public water supplies is assessed by monitoring requirements under EPA’s Total Coliform Rule."

Published studies highlight outbreaks associated with backflow related issues.
Waterborne disease outbreaks caused by distribution system deficiencies
Craun, Gunther F; Calderon, Rebecca L. American Water Works Association. Journal; Denver93.9 (Sep 2001): 64.
Outbreaks caused by cross-connections.
In 1993, two outbreaks of fluoride poisoning were caused by backsiphonage. Symptoms included nausea, diarrhea, abdominal pain, headache, and dizziness. In Mississippi, 34 of 62 restaurant patrons became ill when a faulty feed pump allowed concentrated fluoride solution to be siphoned into a reservoir at one of the town's two treatment plants; concentrations of 40-200 mg/L fluoride were found in tap water (Penman et al, 1999). In Hawaii, nine of 16 people exposed became ill when concentrated fluoride solution was siphoned into drinking water during low pressure caused by a water main break; concentrations of 220 mg/L fluoride were found in the water (Kramer et al, 1996a). In this instance, the fluoride feed pump did not have a backflow valve. 

In 1994, an outbreak of 304 cases of symptomatic illness occurred at a Tennessee correction facility housing 1,290 inmates (Kramer et al, 1996a). Water for the facility was supplied by the municipal water system. Stool specimens from 110 of 423 inmates were positive for Giardia; 10% of inmates were also positive for Entamobea histolytica. The epidemiological investigation was initiated after seven cases of giardiasis were reported during one month. Because increased incidence of diarrheal illnesses was not found among municipal residents, it was initially suspected that contaminated food or homosexual activity might be routes of infection for the prisoners. Water became suspect, however, when it was learned that the facility had experienced a significant fall in water pressure resulting in low pressure for three days. High concentrations of Giardia (581 cysts/L) were found in water samples collected at the facility, and a likely cross-connection with the water system was identified at the facility's wastewater pump station. 

A September 1995 outbreak affecting 148 people at a Wisconsin high school was attributed to a small, round-structured virus (Levy et al, 1998). The school received its drinking water from a community water supply, and contamination of the water system likely occurred when water from a flooded football field was siphoned through submerged hoses. The source of the contamination on the field was not determined.

In two outbreaks of nitrite poisoning in 1995, defective check valves allowed chemicals to contaminate drinking water (Levy et al, 1998). In California, three people at a school became ill after consuming water from a system with a double-check backflow prevention valve that did not meet the industry standard and had badly deteriorated rubber gaskets. Chemicals used to treat a cooling tower and chilling system for the school's air-conditioning unit contaminated the drinking water through this double-check valve. In New Jersey, drinking water was contaminated by boiler-conditioning fluids that flowed through a faulty check valve stuck in the open position. Six people developed acute cyanosis and were diagnosed with methemoglobinemia caused by nitrites in the conditioning fluid. 

In October 1995, 13 people at an Iowa health care facility developed burning in their mouths and flu-like symptoms after drinking water contaminated with a concentrated liquid soap (Levy et al, 1998). Soap dispensers using water pressure had been incorrectly installed in conjunction with the atmospheric vacuum breakers of the faucet assemblies. When a valve on the water supply hose to the soap dispenser was left open, the soap was siphoned into the water system. The vacuum breakers were ineffective because of incorrect installation.

A cross-connection was blamed for an outbreak of Shigella sonnei that occurred in August 1998 at a Minnesota fair (Levy et al, 1998). The outbreak affected 83 people, four of whom were hospitalized. In July 1997, 123 individuals became ill with E. coli 086:H11 after visiting a country club in New Mexico (Levy et al, 1998). A heavy rainstorm and power outage that occurred two weeks before the outbreak were suspected to have contributed to the backsiphonage of contaminated water into the club's water system. 

Water system employees have also been victims of cross-connections (Levy et al, 1998). In October 1998, 10 people became ill because of a temporary cross-connection in an Ohio water company's office building. One stool specimen was found to be positive for Blastocystis hominis and Endolimax nana, suggesting exposure to fecal contamination. 

Contaminated storage facilities blamed for two outbreaks. In November 1993, seven cases of Salmonella typhimurium gastroenteritis were reported in Anderson Township, Mo. (Angulo et al, 1997; Clark et al, 1996a; Clark et al, 1996b). By Jan. 8, 1994, 31 laboratory-confirmed cases of salmonellosis had occurred. It was estimated that 650 people became ill during the waterborne disease outbreak; 15 were hospitalized, and seven died. The outbreak affected 44% of the residents of Gideon, Mo., and 28% of township residents. 

Water samples from the Gideon municipal water system were positive for both total and fecal coliforms, and S. typhimurium was isolated from a city fire hydrant and water storage tank. Investigators concluded that birds had contaminated a municipal water storage tank. The lack of support for drinking water infrastructure repair and maintenance likely contributed to the situation that allowed the contamination to occur. The water system evaluation included the use of a computer model (EPANET) to develop scenarios for transport of contamination. One revealing finding of the investigation came from a survey showing that 31 % of households reported at least one member continued to drink unboiled city water even after being informed that the outbreak was waterborne and tap water should be boiled (Angulo et al, 1997). Reasons for noncompliance with the boil-water order were forgetting (44%) or not believing the notification (25%).

A November 1993 outbreak of Campylobacter jejuni in Minnesota was believed to be associated with contaminated water in a storage tank (Kramer et al, 1996a; Kramer et al, 19966). Although no specific contamination event was identified, the tank had been cleaned in the previous month, and fecal coliforms were found in water from the tank during the investigation. 

Missouri outbreak attributed to contaminated water mains. Between Dec. 14 and 29, 1989, 45 water meters had to be replaced in Cabool, Mo., because of extreme cold weather with temperatures as low as -28 deg C (-18.4 deg F) (Geldreich et al, 1992; Swerdlow et al, 1992). In addition, two large water mains broke and were repaired December 23 and 26.

US outbreaks of cryptosporidiosis
Solo-Gabriele, Helena ; Neumeister, Shondra.
American Water Works Association. Journal; Denver88.9 (Sep 1996): 76

 Alachua County, Fla.. In July 1995, at a camp in Alachua County, Fla., 72 people out of a group of 104 became ill. All symptomatic individuals tested positive for Cryptosporidium.36 The source of contamination was presumed to have been inadequate backflow prevention at the point of distribution. It is suspected that contaminated water from a garbage-can washer backflowed into the camp's kitchen plumbing system. A hose attached to the water supply on the garbage-can washer could have come in contact with wastewater and under negative pressure could have drawn wastewater into the distribution system. Wastewater within the garbage-can washer tested positive for Cryptosporidium oocysts. Since the outbreak, a backflow prevention device has been added to the system, and access to the garbage-can washer area has been restricted.

Multipathogen waterborne disease outbreak onboard a boat—Chicago, 2008
 Epidemiol and Infect 2011;May 19:1–5
Serdarevic F, Black S, Jones R, et al.

We report an outbreak associated with a dinner cruise on Lake Michigan. This took place on the same day as heavy rainfall, which resulted in 42.4 billion liters of rainwater and storm runoff containing highly diluted sewage being released into the lake. Of 72 cruise participants, 41 (57%) reported gastroenteritis. Stool specimens were positive for Shigella sonnei (n=3), Giardia (n=3), and Cryptosporidium (n=2). Ice consumption was associated with illness (risk ratio 2.2, P=0.011). S. sonnei was isolated from a swab obtained from the one of the boat’s ice bins.
Environmental inspection revealed conditions and equipment that could have contributed to lake water contaminating the hose used to load potable water onto the boat. Knowledge of water holding and distribution systems on boats, and of potential risks associated with flooding and the release of diluted sewage into large bodies of water, is crucial for public health guidance regarding recreational cruises.

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