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Quarantine of institutions buy calan 80 mg overnight delivery blood pressure and pregnancy, wards or dormitories can sometimes be of value; strict segregation of infants if measles occurs in an institution discount calan 240 mg amex arrhythmia dysrhythmia. Live measles vaccine should be given 5–6 months later to those for whom vaccine is not contraindicated 120mg calan with visa hypertension heart attack. During measles infection order calan 120mg with amex blood pressure over 200, vitamin A reserves fall rapidly (especially in malnourished children) which further weakens immunity. Vitamin A supplementa- tion at the time of measles diagnosis replaces body reserves, prevents blindness due to corneal ulceration and keratoma- lacia and significantly reduces measles fatality. If vaccine is available, prompt use at the beginning of an epidemic is essential to limit spread; if vaccine supply is limited, priority should be given to young children for whom the risk is greatest. Disaster implications: Introduction of measles into refugee populations with a high proportion of susceptibles can result in devastating epidemics with high fatality rates. Providing measles vaccine to displaced persons living in camp settings within a week of entry is a public health priority. International measures: Persons travelling to measles en- demic areas should ensure that they are immune to measles. Identification—An uncommon bacterial infection; clinical manifes- tations range from none or asymptomatic pulmonary consolidation to localised cutaneous or visceral abscesses, necrotizing pneumonia and/or a rapidly fatal septicemia. It may simulate typhoid fever or tuberculosis, with pulmonary cavitation, empyema, chronic abscesses and osteomyelitis. Diagnosis depends on isolation of the causative agent; a rising antibody titre in serological tests is confirmatory. Direct immunofluorescent micros- copy is 98% specific but only about 70% sensitive compared with culture. The possibility of melioidosis must be kept in mind in any unexplained suppurative disease, especially cavitating pulmonary disease, in patients living in or returned from endemic areas; disease may become manifest as long as 25 years after exposure. Occurrence—Clinical disease is uncommon, generally occurring in individuals with impaired immunocompetence whose non-intact skin had intimate contact with contaminated soil or surface water. Cases have been recorded in many tropical and subtropical areas of Africa, America, Asia, Australia/Pacific Islands, India and the Middle East. In certain areas, 5%–20% of agricultural workers have demonstrable antibodies but no history of overt disease; in Thailand it is considered to be a disease of rice farmers. Various animals, including sheep, goats, horses, swine, monkeys and rodents (plus various animals in zoological gardens) can become infected, without evidence that they are important reservoirs, except in the transfer of the agent to new foci. Mode of transmission—Usually contact with contaminated soil or water through overt or inapparent skin wounds, aspiration or ingestion of contaminated water or inhalation of soil dust. However, years may elapse between presumed exposure and appearance of clinical disease. Period of communicability—Person-to-person transmission has not been proven conclusively. Laboratory-acquired infections may rarely occur, especially if procedures produce aerosols. Susceptibility—Disease in humans is uncommon even among people in endemic areas who have close contact with soil or water containing the infectious agent. Preventive measures: 1) Persons with debilitating disease, including diabetes, and those with traumatic wounds should avoid exposure to soil or water, such as rice paddies, in endemic areas. Control of patient, contacts and the immediate environment: 1) Report to local health authority: No official report, Class 5 (see Reporting). The infection may be slow to respond to treatment and even with 20 weeks of treatment, 10% relapse. Treatment for an inadequate length of time leads to a high probability of relapse. Risk of introduction should be considered when animals are moved to areas where the disease is unknown. Rare and sporadic human infections are reported almost exclusively in those whose occupations involve contact with animals or work in laboratories (e. Infec- tion with Burkholderia mallei, the glanders bacillus, cannot be differen- tiated serologically from infection with B. Prevention depends on control of glanders in equine species and care in handling causative organisms. Identification—A relatively common but rarely serious clinical syndrome with multiple viral etiologies, characterized by sudden onset of febrile illness with signs and symptoms of meningeal involvement. A rubella-like rash characterizes certain types caused by echovi- ruses and coxsackieviruses; vesicular and petechial rashes may also occur. Transient paresis and encephalitic manifestations may occur; paralysis is unusual. Residual signs lasting a year or more may include weakness, muscle spasm, insomnia and personality changes. Various diseases caused by non-viral infectious agents may mimic aseptic meningitis: these include inadequately treated pyogenic meningi- tis, tuberculous and cryptococcal meningitis, meningitis caused by other fungi, cerebrovascular syphilis and lymphogranuloma venereum. Postin- fectious and postvaccinal reactions require differentiation from sequelae to measles, mumps, varicella and immunization against rabies and small- pox; these syndromes are usually encephalitic in type. Leptospirosis, listeriosis, syphilis, lymphocytic choriomeningitis, viral hepatitis, infec- tious mononucleosis, influenza and other diseases may produce the same clinical syndrome, as discussed in individual chapters. Infection by enteroviruses transmitted from the mother is a frequent cause of neonatal fever with neurological signs. In countries that are polio-free, the most prevalent infectious agent causing paralysis is entero- virus 71, responsible for outbreaks of meningitis and paralysis in many countries. Children and adults with B cell deficiencies are subject to chronic relapsing meningitis, usually caused by enteroviruses. Under optimal conditions, specific identification is possible in about half the cases through serological and isolation techniques. Infectious agents—A wide variety of infectious agents, many associated with other specific diseases. In epidemic periods, mumps may be responsible for more than 25% of cases of established etiology in nonimmunized populations. These include coxsackievirus group B types 1–6 and echovirus types 2, 5, 6, 7, 9 (most), 10, 11, 14, 18 and 30, and enterovirus 71. Coxsackievirus group A (types 2, 3, 4, 7, 9 and 10), arboviruses, measles, herpes simplex and varicella viruses, lymphocytic choriomenin- gitis virus, adenovirus and others provide sporadic cases. Leptospira may cause up to 20% of cases of aseptic meningitis in various areas (see Leptospirosis). Seasonal increases in late summer and early autumn are due mainly to arboviruses and enteroviruses, while late winter outbreaks may be due primarily to mumps. Reservoir, Mode of transmission, Incubation period, Period of communicability and Susceptibility—Vary with the specific infectious agent (refer to specific disease chapters). Control of patient, contacts and the immediate environment: 1) Report to local health authority: In selected endemic areas; in many countries not a reportable disease, Class 3 (see Report- ing). If laboratory-confirmed, specify infectious agent; other- wise, report as “cause undetermined”. Therefore, enteric precautions are indicated for 7 days after onset of illness unless a nonenteroviral diagnosis is established. Meningitis due to Hib, previously the most common cause of bacterial meningitis, has largely been eliminated in many industrialized countries through immunization programs.

For people with the myopathic form buy 120 mg calan free shipping pulse pressure 50-60, there are recommendations that can help prevent attacks buy calan 80 mg low price arteriovenous graft. Circumstances to avoid include strenuous exercise purchase calan 120mg with amex arteria mesenterica superior, long periods of time without eating purchase calan 120mg visa hypertension medication drugs, and extreme cold. They should also notify their physician before undergoing general anesthesia, as this can provoke an episode of muscle pain and weakness. Infants and children with the severe infantile hepatocardiomuscular form are susceptible to life-threatening heart problems and typically have shortened lifespans with numerous medical problems. People with the myopathic form of the disease typically live normal lifespans with periodic muscle problems. This form of the disease is usually manageable and allows for a good quality of life. The Counsyl Family Prep Screen - Disease Reference Book Page 53 of 287 Cartilage-Hair Hypoplasia Available Methodologies: targeted genotyping and sequencing. Detection Population Rate* 48% African American 48% Ashkenazi Jewish 48% Eastern Asia 92% Finland 48% French Canadian or Cajun 48% Hispanic 48% Middle East 48% Native American 48% Northwestern Europe 48% Oceania 48% South Asia 48% Southeast Asia 48% Southern Europe * Detection rates shown are for genotyping. One study indicated that 1 in 19 Amish were carriers of the disease and 1 in 1340 Amish babies were born with the disease. It is also more common The Counsyl Family Prep Screen - Disease Reference Book Page 54 of 287 in the Finnish population where 1 in 76 is a carrier and 1 in 23,000 babies has the disease. Infections, particularly those in childhood, should be given close medical attention. Those with extreme immunodefciency may want to consider bone marrow transplantation to ameliorate this symptom. The Counsyl Family Prep Screen - Disease Reference Book Page 55 of 287 Choroideremia Available Methodologies: targeted genotyping and sequencing. Detection Population Rate* <10% African American <10% Ashkenazi Jewish <10% Eastern Asia 75% Finland <10% French Canadian or Cajun <10% Hispanic <10% Middle East <10% Native American <10% Northwestern Europe <10% Oceania <10% South Asia <10% Southeast Asia <10% Southern Europe * Detection rates shown are for genotyping. The condition causes tissues in the back of the eye, namely the retina, photoreceptors, and choroid (a network of blood vessels that lies between the retina and the white of the eye) to degenerate over time. Night blindness is typically the frst symptom, followed by a loss of peripheral vision. These symptoms typically develop before the age of 20, although the rate of degeneration varies greatly from person to person, even among members of the same family. The Counsyl Family Prep Screen - Disease Reference Book Page 56 of 287 How common is Choroideremia? Fresh fruits and vegetables, an antioxidant supplement, and omega-3 fatty acids—provided either through supplements or foods such as fsh—are often recommended by a physician. Treatments for vision loss are similar to those recommended for any visually- impaired person. Counseling may be helpful to cope with the emotional efects of living with decreased vision. People can live long, productive lives with choroideremia, albeit with progressive visual impairment. The Counsyl Family Prep Screen - Disease Reference Book Page 57 of 287 Citrullinemia Type 1 Available Methodologies: targeted genotyping and sequencing. Detection Population Rate* 20% African American 20% Ashkenazi Jewish 50% Eastern Asia 20% Finland 20% French Canadian or Cajun 20% Hispanic 20% Middle East 20% Native American 20% Northwestern Europe 20% Oceania 20% South Asia 20% Southeast Asia 20% Southern Europe * Detection rates shown are for genotyping. Citrullinemia type I is a disease in which ammonia and other toxic substances build up in the blood, causing life-threatening complications shortly after birth. While infants with citrullinemia type I appear normal at birth, within the frst week of life, most will become lethargic and display poor feeding, vomiting, and seizures that often lead to unconsciousness, stroke, increased pressure around the brain, and death if untreated. While there are less severe and later-onset versions of citrullinemia type I, the mutations for which Counsyl screens are associated with the more severe form that afects infants shortly after birth. Citrullinemia type I belongs to a group of diseases known as urea cycle disorders. Under normal circumstances, the body converts that nitrogen to urea, which is then excreted in urine. People with citrullinemia type I are defcient in an enzyme known as argininosuccinate synthase which is needed for this vital process, leading to a buildup of ammonia and other urea cycle byproducts in the The Counsyl Family Prep Screen - Disease Reference Book Page 58 of 287 body. The goals of treatment for citrullinemia type I are to regulate the amount of ammonia in the blood. Children with citrullinemia will need to be monitored closely by a physician specializing in metabolic disorders. Physicians will also monitor and attempt to relieve any excess of pressure around the brain. The prognosis for a child with citrullinemia type I has not been well established. With treatment, these children can survive for an unknown period of time, however they will have signifcant mental and neurological impairment. Detection Population Rate* 96% African American 96% Ashkenazi Jewish 96% Eastern Asia 96% Finland 96% French Canadian or Cajun 96% Hispanic 96% Middle East 96% Native American 96% Northwestern Europe 96% Oceania 96% South Asia 96% Southeast Asia 96% Southern Europe * Detection rates shown are for genotyping. The Counsyl Family Prep Screen - Disease Reference Book Page 60 of 287 People with Batten disease often develop periodic seizures between the ages of 9 and 18. Some people with Batten disease also develop psychiatric problems including disturbed thoughts, attention problems, and aggression. People with Batten disease also show a decline in motor function and may have difculty controlling their own movement. Batten disease is most common in Finland, Sweden, and other parts of northern Europe, but has been seen worldwide. Various medications can be useful for treating seizures, poor muscle tone, sleep disorders, mood disorders, excessive drooling, and digestion. Batten disease causes blindness and a progressive loss of mental and motor function. Detection Population Rate* <10% African American <10% Ashkenazi Jewish <10% Eastern Asia 94% Finland <10% French Canadian or Cajun <10% Hispanic <10% Middle East <10% Native American <10% Northwestern Europe <10% Oceania <10% South Asia <10% Southeast Asia <10% Southern Europe * Detection rates shown are for genotyping. By the age of 10, children typically have lost their vision and develop seizures, mental disability, muscle twitching, and an inability to control muscle movements (ataxia). They will gradually lose their ability to speak and move and will become profoundly mentally disabled. In other parts of Finland, studies have found that 1 in 385 are carriers in Eastern Finland and 1 in 1000 in the capital of Helsinki. Treatments, such as anti-seizure medication, can only address the symptoms as they arise. They will be profoundly mentally disabled and unable to speak or move some time after the age of 10. The average life expectancy is about 20 years, though the lifespan of people with the disease has ranged from 14 to 39 years. The Counsyl Family Prep Screen - Disease Reference Book Page 63 of 287 Cohen Syndrome Available Methodologies: targeted genotyping and sequencing. Detection Population Rate* <10% African American <10% Ashkenazi Jewish <10% Eastern Asia 75% Finland <10% French Canadian or Cajun <10% Hispanic <10% Middle East <10% Native American <10% Northwestern Europe <10% Oceania <10% South Asia <10% Southeast Asia <10% Southern Europe * Detection rates shown are for genotyping.

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Almost unknown in industrialized countries calan 120 mg blood pressure normal karne ka tarika, schistosomiasis infects 200 million people in 76 countries of the tropical developing world cheap calan 240 mg with visa arteria gallery. A Flatworm that spends part of its life in a freshwater snail host causes schistosomiasis purchase 240mg calan amex blood pressure zetia. Multiplying in the snail discount 80mg calan amex blood pressure kidney disease, a microscopic infective larval stage is released that can penetrate human skin painlessly in 30 to 60 seconds. The larvae grow to adulthood and migrate to the veins around the intestines or bladder, where mating occurs. The eggs produced may lodge in these tissues and cause disease, or they are passed out in urine or feces, where they reach fresh water and hatch to infect snails. Multiplication and Life Cycle Free-swimming larvae (cercariae) are given off by infected snails. These either penetrate the skin of the human definitive host (schistosomes) or are ingested after encysting as metacercariae in or on various edible plants or animals (all other trematodes). After entering a human the larvae develop into adult males and females (schistosomes) or hermaphrodites (other flukes), which produce eggs that pass out of the host in excreta. Cercariae 99 Bacteriological Diseases ©11/1/2017 (866) 557-1746 Pathogenesis In schistosomiasis, eggs trapped in the tissues produce granulomatous inflammatory reactions, fibrosis, and obstruction. The hermaphroditic flukes of the liver, lungs, and intestines induce inflammatory and toxic reactions. Host Defenses Host defenses against schistosomiasis include antibody or complement-dependent cellular cytotoxicity and modulation of granulomatous hypersensitivity. In a relatively small proportion of individuals, heavy infections due to repeated exposure to parasitic larvae will lead to the development of clinical manifestations. The distribution of flukes is limited by the distribution of their snail intermediate host. Larvae from snails infect a human by penetrating the skin (schistosomes) or by being eaten (encysted larvae of other trematodes). Diagnosis Diagnosis is suggested by clinical manifestations, geographic history, and exposure to infective larvae. Control As a control measure, exposure to parasite larvae in water and food should be prevented. Clinical Manifestations Signs and symptoms are related largely to the location of the adult worms. Infections with Schistosoma mansoni and S japonicum (mesenteric venules) result in eosinophilia, hepatomegaly, splenomegaly, and hematemesis. Fasciola hepatica, Clonorchis sinensis, and Opisthorchis viverrini (bile ducts) cause fever, hepatomegaly, abdominal pain, and jaundice. Infections with Paragonimus westermani (lungs, brain) result in cough, hemoptysis, chest pain, and epilepsy. Viral gastroenteritis is an infection caused by a variety of viruses that results in vomiting or diarrhea. It is often called the "stomach flu," although it is not caused by the influenza viruses. Many different viruses can cause gastroenteritis, including rotaviruses, adenoviruses, caliciviruses, astroviruses, Norwalk virus, and a group of Noroviruses. Viral gastroenteritis is not caused by bacteria (such as Salmonella or Escherichia coli) or parasites (such as Giardia), or by medications or other medical conditions, although the symptoms may be similar. Your doctor can determine if the diarrhea is caused by a virus or by something else. The affected person may also have headache, fever, and abdominal cramps ("stomach ache"). In general, the symptoms begin 1 to 2 days following infection with a virus that causes gastroenteritis and may last for 1 to 10 days, depending on which virus causes the illness. People who get viral gastroenteritis almost always recover completely without any long-term problems. Gastroenteritis is a serious illness, however, for persons who are unable to drink enough fluids to replace what they lose through vomiting or diarrhea. Infants, young children, and persons who are unable to care for themselves, such as the disabled or elderly, are at risk for dehydration from loss of fluids. Immune compromised persons are at risk for dehydration because they may get a more serious illness, with greater vomiting or diarrhea. The viruses that cause gastroenteritis are spread through close contact with infected persons (for example, by sharing food, water, or eating utensils). Individuals may also become infected by eating or drinking contaminated foods or beverages. Food may be contaminated by food preparers or handlers who have viral gastroenteritis, especially if they do not wash their hands regularly after using the bathroom. Shellfish may be contaminated by sewage, and persons who eat raw or undercooked shellfish harvested from contaminated waters may get diarrhea. Drinking water can also be contaminated by sewage and be a source of spread of these viruses. For example, in the United States, rotavirus and astrovirus infections occur during the cooler months of the year (October to April), whereas adenovirus infections occur throughout the year. Viral gastroenteritis outbreaks can occur in institutional settings, such as schools, child care facilities, and nursing homes, and can occur in other group settings, such as banquet halls, cruise ships, dormitories, and campgrounds. However, some viruses tend to cause diarrheal disease primarily among people in specific age groups. Rotavirus infection is the most common cause of diarrhea in infants and young children under 5 years old. Adenoviruses and astroviruses cause diarrhea mostly in young children, but older children and adults can also be affected. Norwalk and Noroviruses are more likely to cause diarrhea in older children and adults. Generally, viral gastroenteritis is diagnosed by a physician on the basis of the symptoms and medical examination of the patient. The most important of treating viral gastroenteritis in children and adults is to prevent severe loss of fluids (dehydration). Your physician may give you specific instructions about what kinds of fluid to give. Medications, including antibiotics (which have no effect on viruses) and other treatments, should be avoided unless specifically recommended by a physician. Yes, persons can reduce their chance of getting infected by frequent handwashing, prompt disinfection of contaminated surfaces with household chlorine bleach-based cleaners, and prompt washing of soiled articles of clothing. There is no vaccine or medicine currently available that prevents viral gastroenteritis. A vaccine is being developed, however, that protects against severe diarrhea from rotavirus infection in infants and young children. The disease is characterized by vomiting and watery diarrhea for 3 - 8 days, and fever and abdominal pain occur frequently. Immunity after infection is incomplete, but repeat infections tend to be less severe than the original infection.

A blue/purple color reaction within 10 Waterborne Diseases ©6/1/2018 435 (866) 557-1746 seconds is considered a positive oxidase test generic calan 80 mg on line prehypertension and chronic kidney disease. Please note: This method was validated using nutrient agar purchase 240 mg calan fast delivery arrhythmia frequency, if the oxidase reagent is to be dropped directly on colonies cheap 80mg calan otc heart attack jogging, use tryptic soy agar plates because nutrient agar plates give inconsistent results buy discount calan 120 mg arrhythmia heart condition. Note: Timing of the color reaction is critical, as some Gram-positive bacteria may give false positives after 10 seconds. Also, it is important to put just a small amount of the colony on the oxidase dry slide or saturated pad, as too much bacteria can also cause a false positive oxidase test. Trehalose fermentation is determined by inoculating a tube containing 3-10 mL (depending on the size of the tube used - fill about half full) of 0. A change in coloro o of the medium from purple to yellow is considered a positive for trehalose fermentation. An orange color probably indicates the presence of skatole, a breakdown product of indole, and is considered a positive result. Note: If samples are to be archived for further analysis to determine species or hybridization group, from the nutrient agar plate (Section 10. If there is more than one morphological type that is considered to be presumptively positive, record the number of presumptive positives for each morphological type, as well as the total number of presumptive positives. Waterborne Diseases ©6/1/2018 437 (866) 557-1746 Example 1 Number of Number Morphological presumptively Number positively Number of Description positive colonies submitted to confirmed confirmed per volume filtered confirmation Aeromonas steps per 100 mL Type A: Bright yellow, round, 30 6 6 6 opaque Type B: Dull yellow, oval, 20 4 3 3 translucent 9 per Total number of confirmed Aeromonas per sample: 100 mL Example 1 results in 9 confirmed Aeromonas / 100 mL. Example 2 Number of Number Morphological presumptively Number positively Number of Description positive colonies submitted to confirmed confirmed per volume filtered confirmation Aeromonas steps per 100 mL Type A: Dull yellow, round, 40 5 5 20 opaque Type B: Dull yellow, round, 40 5 3 12 translucent 32 per Total number of confirmed Aeromonas per sample: 100 mL Example 2 results in 32 confirmed Aeromonas / 100 mL. If less than 500 mL are filtered, then adjust the reporting limit per 100 mL accordingly. Ampicillin-dextrin agar medium for the enumeration of Aeromonas species in water by membrane filtration. American Public Health Association, American Water Works Association, and Water Environment Federation. American Public Health Association, American Water Works Association, and Water Environment Federation. Evolving concepts regarding the genus Aeromonas: an expanding panorama of species, disease presentations, and unanswered questions. Additional membranes representing the same dilution for each of the respective cultures were placed on brain heart infusion agar as a control. The Dilution/rinse water blank is used to determine if the sample has become contaminated by the introduction of a foreign microorganism through poor technique. Its purpose is to ensure that the results produced by the laboratory remain within the limits specified in this method for precision and recovery. Selective medium—A culture medium designed to suppress the growth of unwanted microorganisms and encourage the growth of the target bacteria. Waterborne Diseases ©6/1/2018 442 (866) 557-1746 Chlorine Section 1 Ton Containers The top line or valve is for extracting the gas, and the bottom line is for extracting the Cl2 liquid. Waterborne Diseases ©6/1/2018 443 (866) 557-1746 Waterborne Diseases ©6/1/2018 444 (866) 557-1746 Chlorine Exposure Limits and Related Information This information is necessary to pass your pre-test. Can be readily compressed into a clear, amber-colored liquid, a noncombustible gas, and a strong oxidizer. Monochloramine, dichloramine, and trichloramine are also known as Combined Available Chlorine. These are the two main chemical species formed by chlorine in water and they are known collectively as hypochlorous acid and the hypochlorite ion. The connection from a chlorine cylinder to a chlorinator should be replaced by using a new, approved gasket on the connector. On 1 ton Chlorine gas containers, the chlorine pressure reducing valve should be located downstream of the evaporator when using an evaporator. This is the liquid chlorine supply line and it is going to be made into Chlorine gas. In water treatment, chlorine is added to the effluent before the contact chamber (before the clear well) for complete mixing. One reason for not adding it directly to the chamber is that the chamber has very little mixing due to low velocities. In addition to protective clothing and goggles, chlorine gas should be used only in a well-ventilated area so that any leaking gas cannot concentrate. Emergency procedures in the case of a large uncontrolled chlorine leak are as follows: Notify local emergency response team, warn and evacuate people in adjacent areas, and be sure that no one enters the leak area without adequate self-contained breathing equipment. Burning of eyes, nose, and mouth, coughing, sneezing, choking, nausea and vomiting, headaches and dizziness, fatal pulmonary edema, pneumonia, and skin blisters. Waterborne Diseases ©6/1/2018 445 (866) 557-1746 Approved method for storing a 150 - 200-pound chlorine cylinder: Secure each cylinder in an upright position, attach the protective bonnet over the valve and firmly secure each cylinder. Waterborne Diseases ©6/1/2018 446 (866) 557-1746 Chlorine Timeline 1879 - This marked the first time that chlorine was applied as a disinfectant. William Soper of England treated the feces of typhoid patients before disposal into the sewer. Prior to this date, chlorine was applied through the use of hydrated lime, chloride of lime, or bleaching powder. The use of chlorine gas was designed by Maurice Duyk, a chemist for the Belgian Ministry of Public Works. The raw water contained a large amount of sewage which was causing sicknesses in the livestock. Johnson implemented chlorine through chloride of lime, and the bacterial content of the water dropped drastically. Darnall became the first to use compressed chlorine gas from steel cylinders, which is an approach still commonly used today. His implementation used a pressure-reducing mechanism, a metering device, and an absorption chamber. He developed a way to push compressed chlorine from cylinders into an absorption tower in which water was flowing opposite the flow of the chlorine. Because the gas flow was opposite the water flow, the chlorine was able to disinfect the water. This marked the first time a commercial chlorination system was installed at a municipal water treatment plant. These standards called for a maximum level of bacterial concentration of 2 coliforms per 100 milliliters. Because chlorination was the main disinfectant at the time, these standards dramatically increased the number of treatment plants using chlorine. Wolman and Enslow discovered the concept of chlorine demand which states that the amount of chlorine needed to disinfect the water is related to the concentration of the waste and the amount of time the chlorine has to contact the water. The other important discovery of 1919 was Waterborne Diseases ©6/1/2018 447 (866) 557-1746 by Alexander Houston. The compound loop principle of chlorinator control was implemented, which is the most recent major discovery in chlorine application. Chlorine is still the most widely used disinfectant in the United States, but other areas of the world are beginning to use other methods of disinfection with increasing frequency. Since chlorine is still widely used, a thorough understanding of how it disinfects and is implemented is important to those interested in water treatment.