Enteric Fever – Part 1 – Typhoid Fever, Enteric Fever (Salmonella typhi), and Vaccination

Typhoid Fever definition

1. Typhoid fever’s name is caused by Salmonella typhi; this is also called enteric fever.
2. Enteric fever is an acute illness characterized by fever, headache, and abdominal discomfort.
3. This is a clinical syndrome characterized by fever, GIT symptoms, and headache.
4. Salmonella infections are divided into:
   1. 1. Typhoidal infection caused by S.typhi.
      2. S.paratyphi generally has a less severe illness and is caused by S. Paratyphi A, B, or C.
      3. Non-typhoidal infection most common in the USA caused by:
         1. S.typhimurium.
         2. S. enteritidis.
      4. Salmonella is quite uncommon in the USA; 70% are acquired from abroad.
      5. Humans are the only source of this infection (S. Typhi and S. paratyphi), and the spread is from person to person or via contaminated foods or water.

Sample

1. Widal test can be done on the serum of the patient.
2. Feces can be used for the culture.
3. A blood culture can be done and is positive in the early stage of the fever.
4. Urine may also be needed for the culture.
5. In a few cases, a bone marrow sample can be cultured.

Precautions

1. Widal test will be positive after 7 to 10 days of the onset of fever.
2. Culture gives the early result to detect the bacilli.

Pathophysiology

1. Typhoid/Enteric  fever is a syndrome that is characterized by:
   1. Fever.
   2. Headache.
   3. Cough.
   4. Splenomegaly.
   5. Leucopenia.

Epidemiology:

1. 1. Salmonella habitat is an animal gut. Predominantly animal pathogens can also cause disease in man.
   2. Foodstuffs from animal sources are important vehicles in the transmission of infection.
   3. Salmonella is found in humans as well as in chickens and eggs.
      1. It spreads by eating the chickens and uncooked eggs.
   4. It spreads only through close contact with an acutely infected person or chronic carrier.
   5. Most cases occur through contaminated foods or water.
   6. This is a global issue with 13 to 17 million cases per year and ∼60,000 deaths per year.
   7. Children under the age of one year are more prone to develop an infection, and the diseases are more severe.
   8. There is increasing antibiotics resistance to this disease.
2. Enteric fever includes typhoid and paratyphoid fever.
   1. Paratyphoid fever is generally mild than typhoid fever.
3. The Salmonella species cause typhoid fever.
   1. Salmonella typhi and S.paratyphi differs from the other species in that man is the only natural host.

Microbiology of Salmonella typhi:

1. 1. Salmonella typhi and S.paratyphi differ from the other species in that human is the only natural host.
   2. salmonella serologically divided into:
      1. Salmonella typhi.
      2. Salmonella cholerae-suis.
      3. Salmonella enteritidis.
         1. Salmonella different from the other types because it lives in the gastrointestinal tracts of animals and infects humans when there is the contamination of food or water with animal feces.
   3. S.Typhi can grow on ordinary media.
   4. From the feces, culture on the MacConkey agar (or Desoxycholate citrate agar) will see pale non-lactose fermenter colonies.
      1. Colonies on Xylose lysine desoxycholate agar show a red color colony with a central black area.
      2. Wilson’s and Blair’s Bismuth sulfite agar shows black metallic colonies due to H₂S production.
   5. S.Typhi are motile due to flagella.
      1. Generally, salmonellae produce acid and gas from carbohydrates except for S.typhi, which does not produce gas.
   6. Summary of Salmonella typhi:
      1. Gram stain negative bacilli (rods). These are seen as single, pairs, and chains.
         1. These are motile.
         2. These are aerobic.
         3. Non-lactose fermenter.
         4. Produce H2S gas.
      2. Colonies are gray and can grow on ordinary media (blood agar).
      3. Selective media are:
         1. Culture may be taken from the feces.
         2. MacConkey agar  = pale non-lactose fermenting coloies.
         3. Desoxycholate citrate agar = pale non-lactose fermenting colonies.
         4. Xylose-lysine desoxycholate agar = observe for red colonies with a black center.
         5. Wilson and Blair’s bismuth sulfite agar = observe black metallic colonies due to H₂S production.
         6. Selenite F and tetrathionate broth for enrichment, then subculture to MacConkey agar.
      4. Their capsules consist of polysaccharides.
      5. These are motile with flagella.

Salmonella has three antigens (Virulence factors):

1. 1. O – antigen is present in the body of bacteria. It is endotoxin and provides antigenic variation.
      1. This resists alcohol extraction and is thermostable.
   2. H – An antigen is present in the flagella of the bacteria.
      1. It provides antigenic variation and motility.
      2. Flagella antigen undergoes variation by gene rearrangement.
   3. Vi –  antigen is the most superficial of the somatic antigen of S. Typhi. Vi means for virulence.
      1. This is a polysaccharide capsule that surrounds the O antigen, thus protecting the bacteria from an antibody attack on the O antigen.
      2. This aids in resistance to antibodies and complement.
         

         Typhoid bacilli structure

Mode of spread:

1. Contaminated food (including meat).
2. Contaminated water supply.
   

   Typhoid fever (Salmonella Typhi), Pathology

3. The incubation period is 5 to 14 days and sometimes is longer (1 to 3 weeks after exposure and includes fever, headache, and abdominal pain).
4. The incubation period for salmonella gastroenteritis is 6 to 72 hours.

Pathogenesis:

1. 1. There are three types of disease:
      1. Enteric fever.
      2. Gastroenteritis.
      3. Septicemia.
   2. This organism crosses the intestinal epithelium (invade the regional lymph nodes) multiply in the macrophagic cells of  Peyer’s patches, mesenteric lymph nodes, and spleen.
   3. The Peyer’s patches inflamed and may ulcerate.
   4. Bacteremia occurs, and the infection spreads to the lungs, gallbladder, kidneys, and CNS.
   5.  Finally, these bacteria settle in various organs.
   6. During this invasion, these bacteria are phagocytosed by the monocytes (mononuclear phagocytes) and can survive intracellularly, so these are called facultative intracellular parasites.
      

      Enteric bacilli intracellular called I/C parasite

      1. Enteric fever is caused by the S.typhi and S. paratyphi A, B, C.
      2. These bacteria cause gastroenteritis, food poisoning, and few special species that may cause septicemia.
      3. Rarely salmonella may cause osteomyelitis, septic arthritis, and other purulent lesions.
         

         Typhoid fever pathogenesis and cycle

Pathology of salmonella (Enteric fever):

The involvement by the salmonella bacteria is in stages.

1. The first week there is bacteremia.
2. There is splenomegaly in the second week, widespread reticuloendothelial system involvement, and foci of necrosis in the liver.
3. In the third week, there is ulceration of peyer patches with intestinal ulcers and bleeding.
4. Lastly, these bacteria colonize in the gallbladder leads to a chronic carrier state.
5. Chronic infection may lead to infection of the joints, bones, meninges, and other sites.
   

   Pathology of the enteric fever (S. Typhi)

Signs and Symptoms

1. The onset of illness is insidious and non-specific, with intermittent fever, headache, and abdominal pain.
2. Salmonella causes four types of diseases:
   1. Typhoid fever.
   2. Sepsis.
   3. Gastroenteritis (diarrhea).
   4. Carrier state.
3. The incubation time is 7 to 14 days ( and the range is 3 to 60 days).
4. The relapse occurs in 5 to 10% of the untreated cases.
5. Salmonella infection is more common in children less than 10 years of age.
6. Prodromal stage: Malaise, headache, cough, sore throat, abdominal pain, and constipation.
   1. Diarrhea is a late symptom and is usually in the third week of illness.
7. Fever: It is constant and ascends in a stepwise pattern.
8. 7 to 10 days: There is  Paek and patients are sicker.
   1. Early diarrhea.
   2. Abdominal distension and cramps.
9. Patients improve after 7 to 10 days.
   1. Untreated cases recover in about 4 weeks.
   2. Symptoms disappear with antibiotics within 3 to 4 days.
10. Relapse may occur after 2 weeks.
11. The gastroenteritis incubation period is 8 to 24 hours.
    1. There are nausea and vomiting.
    2. There is abdominal pain.
    3. There is diarrhea.
       1. Stools are typically loose, moderate volume, and do not contain blood.
       2. Diarrhea is self-limited and may last for 3 to 7 days.
    4. There may be a fever.
    5. Pregnant ladies if get an enteric fever then are more prone to abortion.
    6. This is a self-limiting disease, and recovery is usually within a week.
12. Sometimes S/S may mimic appendicitis or inflammatory bowel disease.
13. Physical findings are: In the early stage, there is abdominal tenderness, hepatosplenomegaly, and scanty maculopapular rash (rose spot).
14. Complications are: There are complication without treatment or even after the treatment, usually after the third week of the disease, like:
    1. Meningitis.
    2. Lobar pneumonia.
    3. Osteomyelitis.
    4. Intesitinal hemorrage.
    5. Intestinal perforation.
    6. By the 4th week of the illness, the patients have gradual improvement, but in the developing countries, 30% of the patients will die.
       1. 10% of the untreated cases will have relapses.
       2. 1% to 2% of the cases in the USA have mortality.
          

          Enteric fever signs symptoms and course of the disease

Complications

1. There may be:
   1. Relapse.
   2. Intestinal Perforation.
   3. Hemorrhage in the GIT.
   4. Myocarditis.
   5. The lungs may show pneumonia picture.
   6. Rarely periostitis.
   7. Most pregnancies end up in abortion.
   8. There may be bacteremia.
   9. Sepsis, when the salmonella enters the bloodstream, will infect the lungs, brain, and bone.
2. Laboratory findings due to complications:
   1. Intestinal hemorrhage may be occult in 20% of the cases; it usually occurs during the 2nd or 3rd week.
   2. It is less common in treated cases.
   3. Intestinal perforation occurs in 3% of the untreated patients.
   4. Relapse occurs in one-fifth of the patients.
   5. Secondary suppurative lesions are seen in the lung (pneumonia), parotid gland (parotitis), and furunculosis.

Carrier state

1. Roughly 30% of the patients become carriers due to persistent infection of the gallbladder.
   1. After the clinical recovery, 5% to 10% of the patients will continue to excrete S.typhi for several months, and these are the convalescent carrier.
   2. 1% to 4% of the patients continue to carry the organisms for >1 year; this is a chronic stage.
2. These people have no active disease and are symptoms free.
3. From the gallbladder, the bacterias are discharged into the intestine constantly and ultimately go out in the feces.
4. The carrier may have cholecystitis and gallstones.
   1. This is difficult to eradicate the carrier of S. Typhi from the gall bladder.
5. Antibiotics are effective in some of the carriers.
6. While in most cases, bacteria persist and give rise to long-term permanent carriers.
7. Some of the carriers require surgical removal of the gall bladder to cure them.
8. Important: Everybody should wash their hands when they come out of the toilet/washroom.
9. Pregnant ladies end up with abortions in enteric fever.

Lab Diagnosis

1. CBC shows:
   1. Low TLC, leucopenia.
2. Culture of blood, bone marrow, intestinal secretion, feces, and urine can be done.
3. Blood culture, positive in the first week of infection in 80% of the cases. But blood culture may reach 90% of the cases, decreasing to 50% in the third week.
   1. For the culture, roughly 10⁵ to 10⁹ organisms are required, but this count may be low in infants and older adults.
      1. This count may be low in patients taking antacids and H₂ receptor blockers.
   2. Blood culture is positive in 80% of the cases in the first week of infection.
   3. Blood culture is considered 100% specific.
   4. Buffy coat may decrease the time for isolation.
   5. This is subcultured on the MacConkey media.
4. Bone marrow culture is more sensitive than the blood culture but is usually not required.
5. These bacteria are:
   1. Non-lactose fermentor.
   2. Motile.
   3. Produce H₂S.
6. If taken, bonemarrow culture will be positive and may have a high yield of up to 90% sensitivity.
7. Stool examination show leucocytes and rarely RBCs.
8. Stool culture will be a positive but not reliable test. This will be positive within the first 7 days of infection.
   1. This is negative in 60 to 70% of the cases during the first week if the patient is untreated, then positive in these patients in the third week.
   2. The chronic carrier may have stool culture positive even up to one year.
   3. Feces cultures on solid selective media:
      1. Desoxycholate citrate agar where there are non-lactose fermenting colonies.
      2. McConkey medium shows non-lactose fermenting colonies.
      3. There is no gas and no fermentation of the sugar.
      4. Xylose lysine desoxycholate agar shows red colonies with a black center.
   4. Laboratory culture findings of salmonella are:
      

      Lab test	Result
      Oxidase test	Negative
      Indol	Negative
      Lactose (nonlactose fermenter)	Negative
      Urease	Negative
      Voges-Proskauer	Negative
      Simmon’s citrate	Positive/Negative
      TSI (Produce H2S)	Positive (except S.typhi is negative)

9. Serologically salmonella has 5 serogroups: A, B, C, D, and E based on O somatic antigen.
   1. Based on H-antigen are 1200 serotypes.
      1. 7 to 10 days antibody to D-somatic antigen appears.
         1. These antibodies against O antigens reach their peak by 3 to 5 weeks.
      2. H-flagellar antibodies appear later on.
10. Widal test:
    1. 1. The widal test was developed in 1896.
       2. Will be positive after 7 to 10 days of infection.
       3. The blood, bone marrow, bile, and stool culture is superior to the widal test for typhoid fever or carrier state diagnosis.
       4. If the culture’s facilities are not available, then the widal test is a valuable tool for the diagnosis.
    2. The titer of O-antibodies 1:80 is suspicious in unvaccinated patients.
    3. The titer of 1:160 is strongly suggestive of infection in unvaccinated individuals.
    4. The titer of 1:40 for Antibody to flagellar-antigen (H) are suspicious in unvaccinated individual.
       1. While 1:160 is strongly suggestive.
    5. Titers are much higher in the vaccinated individual.
    6. Vi antigen for S.typhi is used to screen the carrier. Antibodies to Vi-antigen are positive in only 70 % of the chronic carrier of S.typhi.
    7. Widal test reporting:
       

       Widal test reading and result

11. Typhidot test claimed by the manufacturing companies that it would be positive after 2 to 3 days.
    

    Typhidot interpretation

12. The urine culture may be done and is positive in the case of enteric fever but is less sensitive.
    1. This is positive in the third or fourth week of the infection.
    2. This is done on the MacConkey media.
13. Bacteriophage typing is done to identify the different strains of S.typhi and also Paratyphi.
    1. This is useful for the epidemiological investigation in case of the source of the outbreak.
14. Summary of diagnosis:
    1. Samonella is non-motile.
    2. Biochemical tests show acid and gas formation from the carbohydrate.
       1. S.typhi does not produce gas formation.
    3. Serologically can identify antigens.
       1. O somatic antigen.
       2. H flagellar antigen.
       3. Vi  surface antigen

 Summary of the available lab tests for the diagnosis of Typhoid fever:

Summary of typhoid fever diagnostic tests:

1. White blood cell count: It is low during the first two weeks.
   1. It is decreased from 4000 to 6000/cmm.
   2. 3000 to 5000/cmm during the next two weeks.
   3. 10,000/cmm or more/cmm may suggest perforation or sepsis (suppuration).
2. There may be anemia, and this may be due to bleeding and is hypochromic and microcytic.
3. Blood cultures are positive during the first 10 days, in 90% of the patients and relapse.
   1. <30% are positive after the third week.
4. Stool culture is positive after the 10th day with increasing frequency up to the 4th or 5th week.
   1. Stool culture-positive after 4 months indicates a carrier.
5. Urine culture is positive during the 2nd to 3rd week in 25% of the patients; even the blood culture is negative.
6. Widal test: H and O agglutinins appear in the serum after 7 to 10 days, increase to the peak in 3rd to 5th week, then gradually fall for several weeks; there is no increase during the relapse.
   1. O Antibody appears before the H appears and is usually higher at the beginning.
   2. During convalescence, the H titer becomes higher than the O antibody.
   3. Widal test may be positive in case of vaccination or previous infection.
   4. Early treatment with antibiotics may cause titer to remain low or negative.

Treatment

1. The drug of choice is Ciprofloxacin.
2. Chloramphenicol is also effective, but this may have a serious side effect.
3. Co-trimoxazole is also used and has less serious side effects than Chloramphenicol.

Treatment of the carrier

1. The carriers are asymptomatic.
2. It is documented that the carrier shed S.tryphi in the stool for one year, and is observed in 1 to 3% of these patients.
   1. The gallbladder is the site for persistent infection.
3. It is difficult to eradicate S.Typhi from the gallbladder. Mostly these are permanent carriers.
4. To eradicate carrier infection, prolonged use, and a high dose of the antibiotics are needed.
5. Ampicillin is the drug of choice, but it has to be given in higher doses and prolonged.
6. Chloramphenicol is not good for carriers.
7. Ciprofloxacin has good results.

Control of the disease

1. The Hygenic measure like:
   1. Clean water supply.
   2. Adequate disposal of the sewage material.
   3. Washing of the hands after the defecation. The best is to wash your hands with soap at least three times.
   4. Take care of food handling and processing.
2. For the carriers, give them treatment and advise them to wash hands after the defection.
3. Vaccination should be advised in the family where there is a history of enteric fever.
   1. Injectable vaccine.
   2. The oral vaccine is replacing the injectable vaccines. These are Vi capsular polysaccharides.
      

      Vaccines types used:

      Type of vaccine	Dose of vaccine	Remarks
      Vi capsular polysaccharide (ViCPS) Typhim Vi	25 µg in 0.5 mL I/M given once Booster dose every 2 years	Side effect fever  = 1% The headache  = 1.5 to 3% Local erythema or induration = 7% Not recommended for children <2 years
      Heat killed the whole organism (S.typhi)	0.5 mL I/M = two doses 4 weeks apart Booster 0.1 mL every three years Dose for children 6 months to 10 years = 0.25 mL I/M	Fever = 17 to 29% Headache severe = 10% Pain at the site of injection = 35 to 60%
      Ty21a (Vivotif Berna) This is live oral, attenuated live bacteria	One capsule one hour before a meal Gien for 4 days Booster every 5 years	There are a few sides effects Not given in the immunocompromised patients. Not given in children <6 years of age.

For the layman:

1. Widal test will be positive after 7 to 10 days of typhoid fever.
   1. O antigen indicates an acute infection and early to rise.
   2. H antigen appears late than O antigen and indicates past infection or vaccination.
   3. The titer of  O antigen 1:40 is negative.
      1. The titer of 1:80 is borderline; repeat the widal test after 5 to 7 days.
      2. Rising titer will indicate typhoid fever.
      3. If the level is the same, then less likely for typhoid fever.
   4. Widal test will be negative in the first 3 to 7 days of typhoid fever.
   5. In the first few days, advise blood culture.

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