Enterobacterales are a large order of different types of germs (bacteria) that commonly cause infections in healthcare settings. Examples of germs in the Enterobacterales order include Escherichia coli (E. coli) and Klebsiella pneumoniae. Show
Antibiotic resistance occurs when the germs no longer respond to the antibiotics designed to kill them. Enterobacterales bacteria are constantly finding new ways to avoid the effects of the antibiotics used to treat the infections they cause. When Enterobacterales develop resistance to the group of antibiotics called carbapenems, the germs are called carbapenem-resistant Enterobacterales (CRE). CRE are difficult to treat because they do not respond to commonly used antibiotics. Occasionally CRE are resistant to all available antibiotics. CRE are a threat to public health. In 2020, a taxonomy change was adopted to use “Enterobacterales” as the name of a new scientific order. “Enterobacteriaceae ” are now a family within the “Enterobacterales” order, along with Erwinaceae, Pectobacteriaceae, Yersiniaceae, Hafniaceae, Morganellaceae, and Budvicaceae. Download Adobe Acrobat version of the manual Cdc-pdf[PDF – 6.65 MB] “We never know the worth of water till the well is dry.” Thomas Fuller Introduction One of the primary differences between rural and urban housing is that much infrastructure that is often taken for granted by the urban resident does not exist in the rural environment. Examples range from fire and police protection to drinking water and sewage disposal. This chapter is intended to provide basic knowledge about the sources of drinking water typically used for homes in the rural environment. It is estimated that at least 15% of the population of the United States is not served by approved public water systems. Instead, they use individual wells and very small drinking water systems not covered by the Safe Water Drinking Act; these wells and systems are often untested and contaminated [1]. Many of these wells are dug rather than drilled. Such shallow sources frequently are contaminated with both chemicals and bacteria. Figure 8.1 shows the change in water supply source in the United States from 1970 to 1990. According to the 2003 American Housing Survey, of the 105,843,000 homes in the United States, water is provided to 92,324,000 (87.2%) by a public or private business; 13,097,000 (12.4%) have a well (11,276,000 drilled, 919,000 dug, and 902,000 not reported) [2]. Water Sources Most water systems consist of a water source (such as a well, spring, or lake), some type of tank for storage, and a system of pipes for distribution. Means to treat the water to remove harmful bacteria or chemicals may also be required. The system can be as simple as a well, a pump, and a pressure tank to serve a single home. It may be a complex system, with elaborate treatment processes, multiple storage tanks, and a large distribution system serving thousands of homes. Regardless of system size, the basic principles to assure the safety and potability of water are common to all systems. Large-scale water supply systems tend to rely on surface water resources, and smaller water systems tend to use groundwater. Groundwater is pumped from wells drilled into aquifers. Aquifers are geologic formations where water pools, often deep in the ground. Some aquifers are actually higher than the surrounding ground surface, which can result in flowing springs or artesian wells. Artesian wells are often drilled; once the aquifer is penetrated, the water flows onto the surface of the ground because of the hydrologic pressure from the aquifer. The Safe Drinking Water Act (SDWA) defines a public water system as one that provides piped water to at least 25 persons or 15 service connections for at least 60 days per year. Such systems may be owned by homeowner associations, investor-owned water companies, local governments, and others. Water not from a public water supply, and which serves one or only a few homes, is called a private supply. Private water supplies are, for the most part, unregulated. Community water systems are public systems that serve people year-round in their homes. The U.S. Environmental Protection Agency (EPA) also regulates other kinds of public water systems—such as those at schools, factories, campgrounds, or restaurants—that have their own water supply. The quantity of water in an aquifer and the water produced by a well depend on the nature of the rock, sand, or soil in the aquifer where the well withdraws water. Drinking water wells may be shallow (50 feet or less) or deep (more than 1,000 feet). On average, our society uses almost 100 gallons of drinking water per person per day. Traditionally, water use rates are described in units of gallons per capita per day (gallons used by one person in 1 day). Of the drinking water supplied by public water systems, only a small portion is actually used for drinking. Residential water consumers use most drinking water for other purposes, such as toilet flushing, bathing, cooking, cleaning, and lawn watering. The amount of water we use in our homes varies during the day:
Source Location Water withdrawn directly from rivers, lakes, or reservoirs cannot be assumed to be clean enough for human consumption unless it receives treatment. Water pumped from underground aquifers will require some level of treatment. Believing surface water or soil-filtered water has purified itself is dangerous and unjustified. Clear water is not necessarily safe water. To assess the level of treatment a water source requires, follow these steps:
Well Construction Regardless of the choice for a water supply source, special safety precautions must be taken to assure the potability of the water. Drainage should be away from a well. The casings of the well should be sealed with grout or some other mastic material to ensure that surface water does not seep along the well casing to the water source. In Figure 8.2, the concrete grout has been reinforced with steel and a drain away from the casing has been provided to assist in protecting this water source. Additionally, research suggests that a minimum of 10 feet of soil is essential to filter unwanted biologic organisms from the water source. However, if the area of well construction has any sources of chemical contamination nearby, the local public health authority should be contacted. In areas with karst topography (areas characterized by a limestone landscape with caves, fissures, and underground streams), wells of any type are a health risk because of the long distances that both chemical and biologic contaminants can travel. When determining where a water well is to be located, several factors should be considered:
The overriding concern is to protect any kind of well from pollution, primarily bacterial contamination. Groundwater found in sand, clay, and gravel formations is more likely to be safer than groundwater extracted from limestone and other fractured rock formations. Whatever the strata, wells should be protected from
Also, a well should be located in such a way that it is accessible for maintenance, inspection, and pump or pipe replacement when necessary. Driven wells (Figure 8.2) are typically installed in sand or soil and do not penetrate base rock. They are, as a result, hammered into the ground and are quite shallow, resulting in frequent contamination by both chemical and bacterial sources. Sanitary Design and Construction Once construction of the well is completed, the top of the well casing should be covered with a sanitary seal, an approved well cap, or a pump mounting that completely covers the well opening (Figure 8.3). If pumping at the design rate causes drawdown in the well, a vent through a tapped opening should be provided. The upper end of the vent pipe should be turned downward and suitably screened to prevent the entry of insects and foreign matter. Pump Selection Dug and Drilled Wells Two basic processes are used to remediate dug wells. One is to dig around the well to a depth of 10 feet and install a solid slab with a hole in it to accommodate a well casing and an appropriate seal ( Figures 8.4 and 8.5). The dirt is then backfilled over the slab to the surface, and the casing is equipped with a vent and second seal, similar to a drilled well, as shown in Figure 8.6. This results in a considerable reduction in the area of the casing that needs to be protected. Experience has shown that the disturbed dirt used for backfilling over the buried slab will continue to release bacteria into the well for a short time after modification. Most experts in well modification suggest installing a chlorination system on all dug wells to disinfect the water because of their shallow depth and possible biologic impurity during changing drainage and weather conditions above ground. Figure 8.7 shows a dug well near the front porch of a house and within 5 feet of a drainage ditch and 6 feet of a rural road. This well is likely to be contaminated with the pesticide used to termite-proof the home and from whatever runs off the nearby road and drainage ditch. The well shown is about 15 feet deep. The brick structure around the well holds the centrifugal pump and a heater to keep the water from freezing. Although dangerous to drink from, this well is typical of dug wells used in rural areas of the United States for drinking water. Samples should not be taken from such wells because they instill a false sense of security if they are negative for both chemicals and biologic organisms. The quality of the water in such wells can change in just a few hours through infiltration of drainage water. Figure 8.8 shows the septic tank discharge in the drainage ditch 5 feet upstream of the dug well in Figure 8.7. This potential combination of drinking water and waste disposal presents an extreme risk to the people serviced by the dug well. Sampling is not the answer; the water source should be changed under the supervision of qualified environmental health professionals. Figure 8.9 shows a drilled well. On the left side of the picture is the corner of the porch of the home. The well appears not to have a sanitary well seal and is likely open to the air and will accept contaminants into the casing. Because the well is so close to the house, the casing is open, and the land slopes toward the well, it is a major candidate for contamination and not a safe water source. Springs Springs are common in rolling hillside and mountain areas. Some provide an ample supply of water, but most provide water only seasonally. Without proper precautions, the water may be biologically or chemically contaminated and not considered potable. To obtain satisfactory (potable) water from a spring, it is necessary to
Figure 8.10 illustrates a properly developed spring. Note that the line supplying the water is well underground, the spring box is watertight, and surface water runoff is diverted away from the area. Also be aware that the water quality of a spring can change rapidly. Cisterns Disinfection of Water Supplies The understanding of certain terms is necessary in talking about chlorination. Table_8.4 is a chlorination guide for specific water conditions. Chlorine is the most commonly used water disinfectant. It is available in liquid, powder, gas, and tablet form. Chlorine gas is often used for municipal water disinfection, but can be hazardous if mishandled. Recommended liquid, powder, and tablet forms of chlorine include the following:
Chlorine Carrier Solutions Routine Water Chlorination (Simple) Simple chlorination may not be enough to kill certain viruses. Chlorine as a disinfectant increases in effectiveness as the chlorine residual is increased and as the contact time is increased. Chlorine solutions should be mixed and chlorinators adjusted according to the manufacturer’s instructions. Chlorine solutions deteriorate gradually when standing. Fresh solutions must be prepared as necessary to maintain the required chlorine residual. Chlorine residual should be tested at least once a week to assure effective equipment operation and solution strengths. A dated record should be kept of solution preparation, type, proportion of chlorine used, and residual-test results. Sensing devices are available that will automatically shut off the pump and activate a warning bell or light when the chlorinator needs servicing. Well Water Shock Chlorination With shock chlorination, the entire system—from the water-bearing formation through the well-bore and the distribution system—is exposed to water that has a concentration of chlorine strong enough to kill iron and sulfate-reducing bacteria. The shock chlorination process is complex and tedious. Exact procedures and concentrations of chlorine for effective shock treatment are available [6,7]. Backflow, Back-siphonage, and Other Water Quality Problems Backflow Examples of backflow causes include supplemental supplies, such as a standby fire protection tank; fire pumps; chemical feed pumps that overpower the potable water system pressure; and sprinkler systems. Back-Siphonage
There are many techniques and devices for preventing back-flow and back-siphonage. Some examples are
An air gap, which is a physical separation between the incoming water line and maximum level in a container of at least twice the diameter of the incoming water line. If an air gap cannot be installed, then a vacuum breaker should be installed. Vacuum breakers, unlike air gaps, must be installed carefully and maintained regularly. Vacuum breakers are not completely failsafe. Other Water Quality Problems Protecting the Groundwater Supply
References
Additional Sources of Information American Water Works Association. Available from URL: http://www.awwa.orgExternal. Drexel University: Drinking water outbreaks. Available from URL: http://water.sesep.drexel.edu/outbreaks/. US Environmental Protection Agency: Ground water and drinking water. Available from URL: http://www.epa.gov/safewaterExternal. Table 8.1. Recommended Minimum Distance Between Well and Pollution Sources (Horizontal Distance) [1] Table 8.1
Table 8.2. Types of Wells for Accessing Groundwater, Well Depths, and Diameters Table 8.2
Table 8.3. Disinfection Methods Table 8.3
Table 8.4. Chlorination Guide for Specific Water Conditions
Table 8.5. Preparing a 200-ppm Chlorine Solution Table 8.5
Table 8.6. Analyzing and Correcting Water Quality Problems [8] table 8.6
Page last reviewed: October 1, 2009 Which of the following explains the relationship between plants and their Rhizobial endosymbionts?Which of the following explains the relationship between plants and their endosymbionts, the rhizobia? Plants produce leghemoglobin to bind to and keep the levels of oxygen low, and rhizobia fix nitrogen while residing inside plant cells.
Which of the following are characteristics of cyanobacteria?Cyanobacteria Traits. Eukaryote.. Photosynthetic.. Unicellular and multi-cellular.. Can be filamentous.. Found only in aquatic environments.. Does not produce toxins.. Can form visible colonies in water.. Which of the following genera of organisms forms a beneficial symbiotic relationship with plants?Rhizobium species form a mutually beneficial relationship with certain types of plants.
Which of the following are true regarding coliforms quizlet?Which of the following are TRUE regarding coliforms? they are characteristically ferment lactose; they are facultative anaerobes; they are gram negative; they belong to the family Enterobacteriaceae; they are used as indicators of fecal pollution.
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