| | Infection: Invasion by pathogenic microorganisms of a bodily part in which conditions are favorable for growth, production of toxins, and subsequent injury to tissue.
– American Heritage Dictionary (AHD)
What kind of environment do
pathogens like?
Germs thrive where it is:
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Warm
Where body temperature is ideal |
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Wet
Where there is moisture; in dry places they lose water quickly |
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Dark
Where it is dark; most germs much prefer darkness over light |
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Rich in Nutrients
Where there is food to grow and reproduce |
In other words, inside you!
Now, you might think it's a stroke of bad luck that your digestive tract is an ideal place for pathogens. In fact, the alimentary canal needs to support micoorganisms, because we depend on some of them in our daily digestive processes. They help break food into its components to supply energy or build our bodies. It's an arrangement that benefits both the microbes and us. We provide a home to the "good" bacteria, and they return the favor by helping us digest our food. Problems arise when pathogenic organisms find their way to the same hospitable enrivonment.
How do germs travel?Many pathogenic microorganisms, though not all, can survive for a time outside a host.
However, to thrive (to grow and reproduce quickly) they need all four favorable conditions: warmth, water, darkness, and food. For a species of microorganism to survive, individuals must find a new host or face extinction. The journey from one host to another for many micoorganisms, especially the ones water suppliers are concerned about, is called the fecal-oral route. The pathogens multiply in one host, are excreted from its intestinal tract in solid waste (feces), and must find their way into the digestive tract of another host (through the mouth: oral) before they die from exposure to the elements (light, cold, lack of water or food).
Hand-washing makes a difference
By now, you probably have an idea of how hygiene in general, and hand washing in particular, can reduce the spread of disease. Why is it especially important for health care workers, kitchen workers, or day care providers to practice good hygiene?
The most direct route for bacteria and viruses from one host to another is not to hitch a ride on food or water, but to pass directly from one person to another. This transmission is called direct contact.
Young children, especially, often put their hands or fingers to their mouths. If Robert has a cold or an intestinal illness, and holds hands or shares objects with Justine, the likelihood is high that germs have been passed from him to her. When Justine's hands go to her nose or mouth, the disease has been spread.
Hand washing by either child interrupts the pathway. It is a common sense health practice to wash your hands after using the bathroom, to protect others, or before eating, to protect yourself. If you have a cold or other illness, or are around people who do, it is a good idea to wash your hands more often than usual.
Symptoms of infection?
How do pathogens cause diarrhea? Suppose you have picked up some pathogenic bacteria by touching a contaminated surface or object. You transfer the pathogens from your hands to your sandwich, and then you swallow them. The microbes now have an ideal environment in your intestines, and they reproduce rapidly. They also produce toxins that are very irritating to your intestines. These irritations have the unhappy effect of causing your intestines to lose water. This is diarrhea. Diarrhea often leaves other systems without enough water, a condition called dehydration. People who suffer from diarrhea are vulnerable to dehydration.
Our bodies are designed to fight off disease. Our immune systems can identify pathogens, then make antibodies to attack them. Once the body encounters and resists a pathogen, it "remembers" that event and can call upon those antibodies on short notice. We are then immune to that disease. When we get sick, it is usually because the pathogen is unfamiliar to our immune system and is present in such numbers that the body can't make antibodies quickly enough to prevent infection. Most vaccines prevent disease by introducing materials that trigger antibody formation.
What is water's role?
Under the proper (or rather, improper) conditions, drinking water can provide the link between hosts. An infected individual excretes millions of pathogenic microbes daily, and some of those may find their way into lakes or streams. If other people drink the contaminated water while the microbes are still viable, alive and able to reproduce, more people become infected. If each new case of infection produces ten more cases, the number of sick people increases exponentially (from one to ten to a hundred to a thousand). Such an event is an epidemic, rapid and extensive spread of infection among individuals.
Effective sanitation stops the cycle
The fecal-oral route, from the end of one digestive tract to the beginning of another, can be interrupted by adequate sanitation. Sanitation refers primarily to wastewater and sewage treatment of human waste, but it also refers to systems that treat water between its source in nature and the consumer. The role of wastewater treatment is to collect and process human waste to stop the transmission of pathogens by killing them. Areas with poor sanitation are fertile ground for the spread of disease. Even where sanitation is in place, it can be disrupted by natural events, such as storms or earthquakes, or human events, such as wars, making populations vulnerable to epidemic.
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A special note about Influenza...
What is the flu? Can we get flu from drinking water? Influenza, flu's whole name, is a viral (caused by virus) infection that comes in many strains, all of which can be grouped into types A, B, and C. It is not a gastrointestinal disease, but a respiratory one. That is, we get it by breathing the virus, rather than swallowing it. Its transmission is largely airborne, by coughing and sneezing, though family members could transmit it by direct contact. The term "stomach flu" is a misnomer. |
Surface Water versus Groundwater
MWRA uses surface water collected in reservoirs as its drinking water supply. Other surface water sources include rivers, streams, lakes or ponds. The alternative to surface water is groundwater obtained from wells. Most large cities in the United States rely on surface water, while many smaller towns or individual homes depend on wells. These two sources are quite different with regard to biological contamination. Surface water is almost certain to carry some bacteria; groundwater from properly constructed and maintained wells is almost certain to be free of them. Rain may encounter animal waste on the surface, but as it seeps into the ground, microbes are filtered out by soils, sand and gravel before the water reaches the water table. When it is pumped to the surface, it has undergone nature's filtration.
Surface water is never contaminant freeEven in normal circumstances, surface water bodies are certain to contain at least some fecal organisms. Quabbin Reservoir is about as clean a source of surface water one could find, but before treatment it isn't entirely safe to drink. The animals in the watershed, from bear and beaver to geese and gulls, constantly contribute waste (fecal matter) to the environment, and runoff will certainly carry microbes into streams and thus to the reservoir. If one of the animals carries an organism pathogenic to humans, and people drink that water without taking preventive measures, they are vulnerable to the illness.
Are the people who drink the water certain to get sick? Not at all. Depending on the pathogen, if only one or two such microbes are ingested, hopefully the body's immune system will identify and defeat the invader. If a few more microbes are ingested, that might make some people sick. In other words, if everyone in a group swallows the same dose, some people may get sick while others do not. Despite all the "maybes," one fact is certain: the higher the concentration of pathogens in the water, the more people are likely to get sick.
Water and wild animalsDo wild animals ever get sick by drinking from rivers and ponds?
There are several answers to this question:
- They sometimes do get sick, but we don't always know about it.
- Animals, like humans, tend to seek clean water sources. As you know, clean water is less likely to cary pathogens.
- Different microorganisms make different species sick. A virus that makes human beings sick might not have an effect on a deer or a raccoon.
What can water suppliers do?
So, since microbes are everywhere, what are the protective measures we can take? We have already begun to discuss this in general terms, but let us consider a specific series of barriers that water suppliers can put in place to preclude the spread of disease through drinking water.Keeping pollutants out of source waters
The first barrier is preventive. Minimizing contamination of source waters is called source protection. At Quabbin and Wachusett Reservoirs, human contact with the water is carefully limited. Because people aren't allowed to swim in the reservoir, or camp on its shores, exposure of the water to human pathogens is reduced. If the nearest homes or neighborhoods are some distance away, the chance of material from a leaking sewer line or a malfunctioning septic system reaching the reservoir while still viable (able to cause infection) is greatly reduced. Animal populations are monitored, and bird populations are encouraged not to congregate near any intake structure. In surface water systems, another term for source protection is watershed management, and it is a high priority of MWRA and the Metropolitan District Commission, who manage the reservoirs.
Water treatment removes pollutantsThe next barriers against microbes in surface water are sedimentation (often called clarification) and filtration. All river sources and many reservoirs need clarification and filtration. Only the cleanest, best protected sources are able to skip these processes.
In clarification tanks, a simple chemical is often added to encourage small particles, whether soil or vegetation or micoorganisms, to clump together. Then they either settle at the bottom or float to the top, leaving the water much cleaner. MWRA does not have clarification tanks now, though we may in the future. Our water resides so long in Quabbin and Wachusett Reservoirs that natural sedimentation cleans the water effectively.
In filtration systems, water seeps through layers of sand or other materials, imitating nature's filtration of groundwater. If a filter has small enough pores, water will seep through, but solid particles, including microorganisms, will be screened out. At this time, MWRA water from Quabbin and Wachusett Reservoirs is not filtered, though that too may change in years to come.
Disinfection kills bacteria
The final barrier, also to eliminate pathogens from the water, is called disinfection. Disinfection can be accomplished in two ways: by heat or by chemicals. If water is boiled, most microorganisms in it will not survive. They aren't removed, but since they are no longer alive, they won't make you sick. Boiling can be an effective disinfection practice on a small scale, such as when camping or in an emergency, but on a large scale, such as municipal water supply, its energy costs would be enormous. Water suppliers use chemical disinfection to deactivate (kill) microorganisms. Chlorine is the most common chemical disinfectant, but ozone is also an important option. The MWRA presently uses chlorine to disinfect, adding a small amount of ammonia to preserve the disinfectant effect as the water travels through aqueducts and pipes to the consumer.All these barriers have costs. Water suppliers must consider the quality of both their source and treated ("finished") water, as well as cost, to decide which form of protection is best.
What are the rules?
A strict set of standards guides the drinking water industry. The underlying rule for germs is that there should be no fecal organisms in the water. Testing procedures and proper water treatment are carefully defined and enforced.
The Safe Drinking Water Act (SDWA) was enacted in 1974 by the US Congress; it was revised and updated in 1986 and 1996. The US Environmental Protection Agency (EPA) enforces SDWA by requiring each state to designate an agency to oversee its water suppliers. States may make certain provisions of their laws more strict than SDWA, but no one can change SDWA rules to make them more lenient.
In Massachusetts, SDWA is enforced by the Department of Environmental Protection (DEP). Public water suppliers in Massachusetts must report regularly to DEP concerning the withdrawals from their sources, the quality of their source water, and the analysis of the finished water they deliver to consumers.
Conclusion
We hope you now know a little more about germs and a lot more about water. It's important to understand how pathogenic microorganisms live and function, and how they can be passed from one person to another. Since water is as important to microbes as it is to us, it can serve as a pathway from one host to another. Water treatment protects us in two ways: by cleaning wastewater before it reenters the environment, and by cleaning drinking water between its source in the environment and the consumer. Water suppliers must conform to a strict set of standards, not only because they are required to, but because they take seriously their role in protecting public health.Not all diseases are gastrointestinal, and even among those that are, water is not always the risk factor. We conclude with a list of diseases, the microbes that cause them, and comments about their routes of exposure. Go to Diseases and their pathogens to see the list.
A Final Note On E. Coli
"The rod-shaped bacteria known as E. coli are part of the normal flora of our intestines.... The vast majority of E. coli strains are harmless to most humans most of the time.... There are five groups of E. coli whose toxins cause diarrhea of various levels of severity. Some are the culprits behind traveler's tummy or "Montezuma's revenge." One country's flora are different from another's, so tourists may suffer a kind of poisoning until their immune systems adapt to newly imbibed bacteria."The worst E. coli bacterium, E. coli 0157:H, a mutation discovered in 1982 that has at least 62 subtypes, causes hemorrhagic colitis, an acute bloody diarrhea much like dysentery that can kill weak victims. Undercooked beef and raw milk are the microbe's favorite homes.... In 1991, twenty-seven people in Massachusetts were struck with ECO157 infection after drinking cider made from apples grown on trees fertilized with manure."
 | [Note about apple cider: The E. coli did not infect the apples on the tree. Cider is often made from "drops," apples that have fallen to the ground. If the "drops" come in contact with manure applied to the trees, contamination can occur.] |
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