Typhoid fever

　　Whether a person develops typhoid fever after infection with Salmonella typhi is related to factors such as the number of bacteria, virulence, and immune function of the body. Factors such as low gastric acid, severe malnutrition, anemia, and hypoproteinemia are also factors that can cause typhoid fever.

　　Salmonella typhi is the causative agent of the disease. Salmonella typhi has strong vitality in the natural environment, surviving in water for 2 to 3 weeks and in feces for 1 to 2 months. It can withstand low temperatures and maintain viability for several months in frozen environments. Its resistance to sunlight, dryness, heat, and disinfectants is weak, and it can be killed by direct sunlight within a few hours; it dies immediately when heated to 60°C for 30 minutes or boiled; it is also killed within 5 minutes in a 3% phenol solution; the residual chlorine in water at 0.2 to 0.4 mg/L can quickly kill it; it can survive and even reproduce in food (such as milk).

　　Salmonella typhi only infects humans and does not infect animals under natural conditions. Salmonella typhi does not produce exotoxins, and when the bacterial body is lysed, it releases endotoxins, which play an important role in the pathogenesis of the disease.

　　The complications of typhoid fever are complex and diverse, with varying incidence rates. The same patient may simultaneously or sequentially develop multiple complications.

　　1. Hemorrhagic colitis is a common serious complication, with an incidence rate of about 2.4% to 15%, most commonly seen in the 2nd to 3rd week of the disease course, ranging from occult blood in stool to massive bloody stools. Small amounts of bleeding may be asymptomatic or only accompanied by mild dizziness and a rapid pulse; in cases of massive bleeding, the body temperature drops suddenly, the pulse becomes rapid and thin, and there is a cross phenomenon between the body temperature and pulse curve, along with dizziness, pale complexion, irritability, cold sweat, and a decrease in blood pressure. Patients with diarrhea have a higher chance of developing intestinal hemorrhage. Excessive physical activity, inappropriate dietary composition, overly coarse food, overeating, excessive force during defecation, and inappropriate therapeutic enemas can all be triggers for intestinal hemorrhage.

　　2. Intestinal perforation is the most serious complication, with an incidence of about 1.4％～4％, most common in the 2nd to 3rd week of the disease course, intestinal perforation often occurs in the distal ileum.

　　3. The incidence of toxic myocarditis is 3.5％～5％, common in the 2nd to 3rd week of the disease course in patients with severe toxicosis, clinical features include tachycardia, weakened first heart sound, irregular heartbeat, premature ventricular contractions, diastolic gallop rhythm, low blood pressure, ECG shows prolonged P-R interval, T wave changes, S-T segment shift, etc., these symptoms, signs, and ECG changes usually return to normal with the improvement of the condition.

　　4. The incidence of toxic hepatitis is about 10％～68.5％(most of them are 40％～50％), common in the 1st to 3rd week of the disease course, the main feature is liver enlargement, may be accompanied by tenderness, mild elevation of alanine aminotransferase activity, even mild jaundice, severe cases may threaten life.

　　5. Bronchitis and pneumonia are more common in the early stage of the disease; pneumonia (bronchopneumonia or lobar pneumonia) usually occurs in the acute phase and late stage of the disease course, mostly secondary infection, rarely caused by Salmonella typhi, severe toxicosis may have tachypnea, tachycardia, and cyanosis, cough is not prominent, physical examination may find lung rales and/or signs of lung consolidation.

　　Typhoid fever can be diagnosed clinically based on epidemiological data, clinical course, and immunological examination results, but the diagnosis of typhoid fever is based on the detection of the pathogenic bacteria, the incubation period is 5～21 days, and the length of the incubation period is related to the amount of the infecting bacteria.

　　The natural course of typical typhoid fever is about 4 weeks, which can be divided into 4 stages. The symptoms of the four stages are also different from each other.

　　(1)Early stage: Corresponds to the 1st week of the disease course, the onset is usually gradual, fever is the earliest symptom, often accompanied by general discomfort, fatigue, decreased appetite, headache, discomfort in the abdomen, etc., the condition gradually worsens, body temperature rises step by step, and can reach 39～40℃ in 5～7 days, there may be chills before fever, few cases have shivering, sweating is not much, and at the end of this period, the enlarged spleen and liver can often be palpated.

　　(2)Acute phase: During the 2nd to 3rd week of the course of the disease, typical symptoms of typhoid fever often occur, complications such as intestinal hemorrhage and intestinal perforation also occur frequently during this period, and the disease manifestation has been fully displayed.

　　①High fever: Relapsing fever is a typical fever pattern, a few may present with remittent or irregular fever patterns, high fever usually lasts for about 2 weeks, the peak can reach 39～40℃, and there may be cases over 40℃.

　　②Gastrointestinal symptoms: Lack of appetite, abdominal distension, discomfort or hidden pain in the abdomen, more prominent in the lower right abdomen, may also have mild tenderness, usually presents with constipation, a few may have diarrhea.

　　③Symptoms of nervous and mental system: Generally closely related to the severity of the disease, patients are weak, mentally confused, expressionless,呆滞, slow in response, hearing impairment, severe cases may present with delirium, coma, and may also show symptoms of pseudomeningitis, these symptoms are all related to severe toxic blood symptoms, and the condition will gradually improve and recover with the decrease in body temperature.

　　④ Circulatory system symptoms: There is often a relative bradycardia (pulse rate does not match the rise in body temperature) or tachycardia. If myocarditis is present, relative bradycardia may not be obvious.

　　⑤ Hepatosplenomegaly: During this period, the enlarged spleen can often be palpated, soft, with mild tenderness, and liver enlargement may also be found, soft, with tenderness. Hepatosplenomegaly is usually mild, gradually returns to normal with the recovery of the condition. In cases of significant toxic hepatitis, jaundice, elevated alanine aminotransferase, and other liver function abnormalities may be seen.

　　⑥ Rash: During the 7th to 12th day of the course, some patients may develop pale red maculopapular rash (rosa spots), with a diameter of about 2-4mm, fades under pressure, slightly elevated above the skin surface, not many, usually around 10, appearing in batches, distributed more in the chest and abdomen, also seen on the back and limbs, usually subsides 2-4 days later. In addition, patients with excessive sweating may have crystal-like prickly heat (white pustules).

　　(3)Remission period: During the 3rd to 4th week of the course, body temperature begins to fluctuate and gradually decrease, the patient still feels weak, appetite begins to recover, abdominal distension decreases, the enlarged spleen retracts, tenderness decreases. Various complications may still occur during this period, including intestinal hemorrhage, intestinal perforation, and other serious complications can still occur.

　　(4)Convalescence period: During the 5th week of the course, body temperature returns to normal, appetite improves, symptoms and signs return to normal. It usually takes about a month to completely recover.

　　Medicine shows that the key to preventing typhoid is to strengthen food, drinking water, and feces management, interrupt the transmission route, isolate patients and carriers as intestinal infectious diseases until one week after drug discontinuation, perform fecal cultures weekly, and stop when two consecutive negative results are obtained. The protective effect of the long-used inactivated vaccine is not ideal, and live-attenuated vaccines are being tested.

　　The prevention of this disease should adopt comprehensive preventive measures with the focus on interrupting the transmission route, adapted to local conditions.

　　1. Control the source of infection

　　2. Isolate and treat patients early, the isolation period should be until the disappearance of clinical symptoms and the normalization of body temperature for 15 days, and also conduct fecal culture tests, 1 time/5-7 days, those who are negative for two consecutive times can be released from isolation. The patient's feces, toilet, tableware, clothing, daily necessities must be appropriately disinfected. The management of chronic carriers should be strictly enforced, and personnel in industries such as catering, child care, and water supply should be regularly checked to detect carriers early. Chronic carriers should be transferred from the above positions, treated, and regularly supervised. Close contacts should be under medical observation for 23 days, and suspected typhoid patients with fever should be isolated and treated early.

　　2. Interrupt the transmission route

　　Key measures to prevent this disease include health education, good sanitation of feces, water sources, and food, elimination of flies, fostering good hygiene habits, washing hands before meals and after defecation, not eating unclean food, not drinking unfiltered water, raw milk, etc., improving water supply sanitation, strictly enforcing water sanitation supervision, which is the most important link in controlling the spread of typhoid. The waterborne spread of typhoid is the most important in many regions, and after the improvement of water supply sanitation, the incidence rate can decrease significantly.

　　3. Protect susceptible individuals

　　Typhoid vaccination can provide some protection for susceptible populations. The trivalent vaccine for typhoid, paratyphoid A, and B is not yet ideal in terms of preventive efficacy and has a significant reaction, so it is not used as a routine immunoprophylactic measure. There is no consensus on emergency immunization issues in outbreak areas, and it may have a certain effect on controlling the epidemic. The Ty21a strain of oral attenuated live vaccine was approved for use in the United States in 1989, with fewer adverse reactions and some protective effect.

　　(One) Routine Examination

　　Including blood tests, urine, and stool examinations. Blood tests: The total white blood cell count is usually reduced, about (3～5)×10^9/L, with a decrease in neutrophils accompanied by left shift of the nucleus, a relative increase in lymphocytes and monocytes, and a decrease or disappearance of eosinophils. Urine: Patients with high fever may have mild proteinuria and occasionally a few casts. Stool: In cases of intestinal bleeding, there may be occult blood in the stool or hematochezia.

　　(Two) Bacteriological Examination

　　① Blood culture is the evidence for diagnosis, which can be positive in the early stage of the disease. The positive rate reaches 90% in the 7th to 10th day of illness, decreases to 30% to 40% in the third week, and is often negative in the fourth week;

　　② Bone marrow culture has a higher positive rate than blood culture and is particularly suitable for patients who have been treated with antibiotics and have negative blood cultures;

　　③ Stool Culture: Positive results can be obtained from the incubation period, with a rate as high as 80% in the 3rd to 4th week. The positive rate decreases rapidly after 6 weeks, and 3% of patients may excrete bacteria for more than a year;

　　④ Urine Culture: The positive rate can reach 25% in the late stage of the disease, but it should be avoided to contaminate the stool;

　　⑤ The scraping of rose spots or biopsy slices can also yield positive cultures.

　　(Three) Immunological Tests

　　1. Widal Test: The Widal serum agglutination test, or Widal reaction, is positive in typhoid fever and paratyphoid fever, which has auxiliary diagnostic value for these diseases.

　　2. Other Immunological Tests

　　(1) Passive Hemagglutination Test (PHA).

　　(2) Counterflow Immunoelectrophoresis (CIE).

　　(3) Coagulation Agglutination Test (COA).

　　(4) Immunofluorescence Test (IFT).

　　(5) Enzyme-Linked Immunosorbent Assay (ELISA).

　　(Four) Molecular Biological Diagnostic Methods

　　1. DNA Probe (DNA Probe): DNA probes are diagnostic reagents prepared from DNA, used for detecting or identifying specific bacteria.

　　2. Polymerase Chain Reaction (PCR): PCR is a molecular biological method that developed in the mid-to-late 1980s.

　　Points to note in terms of diet for patients with typhoid fever:

　　1. During the high fever stage, fluid and semi-liquid diets such as rice porridge, egg custard, lotus root starch, vegetable puree, and fruit juice should be consumed. Drinking plenty of water helps replenish body fluids and aids in cooling and detoxification.

　　2. During the remission period, the appetite of patients improves, but due to the risk of intestinal bleeding and perforation at this stage, it is necessary to adopt easily digestible, low-fiber, and soft foods. Foods rich in rough fiber and those that stimulate intestinal motility and bloating should be avoided. It is not advisable to drink milk, soy milk, sucrose, sweet potatoes, and other gas-producing foods.

　　3. Patients in the recovery period should gradually transition from semi-liquid, low-fiber, soft drinks to ordinary diet. In principle, high-energy, high-protein, and high-carbohydrate foods should be eaten.

　　A. The energy intake should generally be controlled at 2000-2400 kcal or more.

　　B. Carbohydrates should be the main component.

　　C. The protein supply should be higher than that of healthy people,

　　D. It is advisable to eat high-quality foods such as milk, eggs, liver, lean meat, and soy products.

　　E. Fat should be moderate, and vegetable oil should be used for cooking.

　　F. Provide abundant vitamins and minerals.

　　G. Eat in small and frequent meals, and the diet should be light and easy to digest.

　　4. In principle, chickens, fish, meat, and eggs of typhoid fever patients in the recovery period can be eaten, but it is best not to use frying or frying methods. The consumption of garlic should also be increased gradually from less to more.

　　For patients with general treatment and symptomatic treatment, isolation for gastrointestinal infectious diseases should be implemented upon admission. After the clinical symptoms disappear, fecal culture should be sent for examination every 5-7 days, and isolation can be lifted after two consecutive negative results.

　　Patients in the fever stage must rest in bed, and they can sit on the bed slightly for 2-3 days after the fever subsides. They can engage in mild activities after 2 weeks of fever subsidence. They should be provided with high-calorie, high-nutrition, easy-to-digest food, including sufficient carbohydrates, proteins, and various vitamins to supplement the consumption during the fever period and promote recovery. During the fever period, it is advisable to use liquid or soft, non-gritty food, and eat in small and frequent meals. After the fever subsides and appetite increases, they can gradually start with congee and soft rice, and avoid eating hard and gritty foods to prevent intestinal bleeding and perforation. Generally, it takes 2 weeks after the fever subsides to return to normal diet. It is encouraged to drink plenty of water, about 2000-3000ml per day (including food), to facilitate the excretion of toxins. If the patient is too ill to eat, 5% glucose physiological saline can be administered intravenously.

　　Patients with severe sepsis can use hormones under the配合 of sufficient effective antimicrobial treatment. If typhoid fever is complicated with schistosomiasis, especially acute schistosomiasis, it is generally advisable to use adrenal cortical hormones in combination with the pathogenic treatment of typhoid fever first, and then oral praziquantel treatment for schistosomiasis after the body temperature is controlled and the overall condition is significantly improved.