What is salmonella?
Salmonella bacteria cause much of the food poisoning in the world, including an estimated four million cases of salmonellosis in the United States each year. In Illinois about 1,500 to 2,500 cases of this foodborne illness are reported each year.
Salmonella is a general name for a group of about 2,000 closely related bacteria that cause illness by reproducing in the digestive tract. Each salmonella subgroup, or serotype, shares common antigens and has its own name.
How is it spread?
Salmonella bacteria is found wherever animals live. The bacteria can withstand hot and cold weather, rain and drought. Animals consume salmonella from the soil or contaminated processed feed. The bacteria are then shed alive in the infected animal's feces. The animal may or may not be sick, depending on the bacteria's serotype.
During slaughtering and processing, salmonella may contaminate animal carcasses. According to U.S. Department of Agriculture estimates, nearly 40 percent of the American poultry supply, 12 percent of the pork and 5 percent of the beef are contaminated with salmonella.
In recent years, fresh fruits and vegetables have been implicated in outbreaks of salmonellosis. Tomatoes were identified as the culprit in 1990 and 1993 and, in 1990 and 1991, cantaloupes were linked to salmonellosis. Investigations of these incidents did not identify the source of contamination. It possibly could have occurred in the fields where the produce was grown, during processing after harvest or during handling in the distribution system.
Person-to-person transmission of salmonella occurs when a carrier's feces, unwashed from his or her hands, contaminates food during preparation or through direct contact with another person. Usually the illness comes from food contaminated with animal feces found on or in raw meats, eggs, fish and shellfish and, most commonly, in poultry. Salmonella also may be found in raw milk or in milk that is contaminated after pasteurization. The bacteria also may be carried by pets birds, fish, dogs, cats and turtles. The U.S. Food and Drug Administration banned the sale of turtles smaller than 4 inches wide in 1975 to prevent the spread of salmonella.
Since early 1950, farmers have administered low doses of penicillin and tetracycline to cows, chickens and pigs to prevent infection and promote growth. As a result, the bacteria in these animals develop a resistance to the drugs. When these drugs are used to treat infections in humans who have eaten meat from treated animals, the drugs are not as effective as they might be. The U.S. Centers for Disease Control and Prevention estimates that between 20 percent and 30 percent of all salmonella cases involve bacteria resistant to antibiotics.
What are the symptoms?
A person may contract salmonellosis many times in his or her life and not always recognize it. Often it is mistaken for the "stomach flu." Symptoms, which last from 24 hours to 12 days, include headache, muscle aches, diarrhea, vomiting, rumblings in the bowels, chills, fever, nausea and dehydration. They usually appear six to 72 hours after ingestion, but carriers have no symptoms. Children younger than 1 year old, people who have had ulcer surgery or take antacids and those whose immune systems have been weakened by other ailments are most susceptible.
Salmonellosis is seldom fatal (the fatality rate is less than 1 percent). Two or three weeks after being infected with salmonella, one in 10,000 cases develops reactive arthritis or Reiter's syndrome as a complication. These patients also may develop an inflammation of the urethra and eyes.
How is salmonellosis treated?
Fluids are recommended to prevent dehydration because the diarrhea that flushes bacteria out of the body drains a great deal of liquid. Pain relievers and fever reducers may make the person more comfortable.
Most cases of salmonellosis are not treated with antibiotics. In fact, antibiotics may prolong the period during which the person can infect others. Also, antibiotics actually may bring on salmonellosis symptoms by upsetting the bacterial balance in the intestines. Antibiotics sometimes are prescribed for infants, the chronically ill and the elderly to prevent salmonella-triggered local infections or bacteremia. Antibiotics also are needed when the bacteria cause meningitis or infections of the blood stream.
Can salmonellosis be prevented?
People are far more likely to contract salmonellosis at home than in a restaurant, so be sure to handle food safely.
Salmonella are killed when food is thoroughly cooked. This means cooking ground beef to at least 155 degrees and making sure all food is cooked properly. Once cooked, any food held in a buffet should be kept hotter than 140 degrees. Cross-contamination--where food is contaminated in the kitchen after it has been cooked--may be avoided by using different utensils, plates, cutting boards and counter tops before and after cooking. Cooked food that stands at room temperature for a long time, especially poultry, is at risk.
Defrost frozen food in the refrigerator or microwave. Refrigerator temperatures should be kept colder than 40 degrees. Rinse poultry in cold water before cooking. Avoid raw milk, raw hamburger meat and raw eggs (many recipes, such as those for homemade ice cream, call for eggs with no subsequent cooking; substitute pasteurized eggs in these recipes). Food contaminated with salmonella may look, smell and taste normal.
Because fruits and vegetables have now been identified as a source of salmonella, it is important that these food items be thoroughly washed in running water before they are eaten.
Wash utensils and wooden cutting boards thoroughly with hot, soapy water. Salmonella may lie dormant for a year or more and then "wake up" when food is present. They also may live in the cut marks on a wooden cutting board. Use an acrylic board that can go in the dishwasher. Rub down or spray wooden boards with a solution of one ounce bleach to one gallon water and allow to air dry. Cutting boards for raw meat and poultry should not be used for cheese, raw vegetables and other foods that will not be cooked before being served.
To prevent the spread of salmonella, wash hands thoroughly after using the bathroom and before handling food. Do not allow an infected person to handle food or work in the kitchen.
一、概述
1885年沙门氏等在霍乱流行时分离到猪霍乱沙门氏菌，故定名为沙门氏菌属。沙门氏菌属有的专对人类致病，有的只对动物致病，也有对人和动物都致病。沙门氏菌病是指由各种类型沙门氏菌所引起的对人类、家畜以及野生禽兽不同形式的总称。感染沙门氏菌的人或带菌者的粪便污染食品，可使人发生食物中毒。据统计在世界各国的种类细菌性食物中毒中，沙门氏菌引起的食物中毒常列榜首。我国内陆地区也以沙门氏菌为首位 。
二、流行病学
(一) 流行概况
世界上最大的一起沙门氏菌食物中毒是1953年于瑞典,由吃猪肉而引起的鼠伤寒沙门氏菌中毒，7717人中毒，90人死亡。由于沙门氏菌型、菌株不同，使人发病的菌量也不同，一般使人发病的菌量平均为107以上。鼠伤寒沙门氏菌是最常见的血清型，在国外占27.7-80%，其次为肠炎沙门氏菌占有10.3%。
(二) 分布
沙门氏菌分布很广，广泛在于自然界中，常可在各种动物，如猪、牛、羊、马、等家畜及鸡、鸭、鹅、等家禽，飞鸟、鼠类等野生动物的肠道中发现。鸡是沙门氏菌最大的储存储主，鸡群暴发死亡率高达80%，也存在于蛋类、蛋粉及其它食物中(牛肉、猪肉、鱼肉、香肠、火腿等)。
(三) 传播途径
大多通过吃进被沙门氏菌污染的食品，吃感染了沙门氏菌的动物内脏及蛋，人传给人。
1、肉的污染：肉及其制品的沙门氏菌检出率美国为20-25%、英国为9.9%、日本检查进口家禽的污染率为10.3%、 国内肉类沙门氏菌检出率在1.1-39.5%。牛、马、猪感染多呈全身丁当，形成败血症。因此吃死牲畜多引起食物中毒型沙门氏菌感染。
2、蛋的污染：我国蛋及其制品沙门氏菌检出率为3.9-43.7%，由于吃蛋引起鼠伤寒病的病例报告逐渐有增加的趋势。
3、环境污染：食品在加工、运输、出售过程中往往被沙门氏菌污染。沙门氏菌在粪便、土壤、食品、水中可生存5个月至二年之久。
4、传播问题：恢复期病人和无症状的带菌者也是常见的传染源。
三、生物学特性：
1、型态与染色：本属菌为1-3um长，0.5-1um宽，需氧的革兰氏阴性无芽胞杆菌，除鸡沙门氏菌外都有周身鞭毛，能运动，多数有菌毛。
2、培养物特性：营养要求不高，在普通培养基上即可生长，在液体培养基中呈均匀混浊生长。在SS琼脂和麦康凯琼脂培养基上37℃24小时可形成直径约为2-4mm的半透明菌落，对胆盐耐受。
3、抗原结构：沙门氏菌具有复杂的抗原结构，主要有三种抗原，即菌体抗原、鞭毛抗原和表面抗原。沙门氏菌的分类原则是以菌体抗原为基础分成群，每群中再以鞭毛抗原来分型。
菌体抗原：即为O抗原，是细菌细胞壁上的脂多糖，能耐热100℃达数小时不破坏。
鞭毛抗原：即H抗原，是蛋白，不稳定，加热或酒精处理都能被破坏。
表面抗原：表面抗原有两种即Vi及M抗原。
4、致病性：伤寒沙门氏菌，甲、乙、丙型副伤寒沙门氏菌和仙台沙门氏菌等只对人类致病，而马流产沙门氏菌，雏沙门氏菌只 对马和鸡致病。可引起如下类型的疾病。
(1) 肠热症：即伤寒(伤寒沙门氏菌引起)和副伤寒(甲、乙副伤寒沙门氏菌引起)。本病的潜伏期为7-20天，伤寒的病程可达一个月，副伤寒病程稍短，目前所见肠热症的临床表现常以轻型和不典型为主。伤寒与副伤寒的鉴别诊断有赖于细菌检验。病后约有2/3的伤寒病人，可发展成慢性带菌者。
(2)食物中毒：一般引起胃肠炎，即上吐下泻。引起食物中毒的沙门氏菌以鼠伤寒、肠炎、汤卜逊、猪霍乱及乙型、丙型副伤寒沙门氏菌等常见。由于食入含有大量细菌的食物而引起，潜伏期为8-48小时，有恶心、呕吐、腹泻、腹痛、发烧等症状，病程 2-5天，重者可持续几个星期。
(3)慢性肠炎：临床上表现为发烧，粘液便，类似痢疾。此病多见于幼儿和老年人。
(4)败血症：多由猪霍乱沙门氏菌引起，病人有高烧、寒战、厌食和贫血等症状，常伴有局部病灶(如胆囊炎等)，一般可从血液中分离出病原菌。