Enteric Fever:- part 4 – Paratyphoid Fever, Salmonella Paratyphi, Diagnosis and Treatment

Salmonella paratyphi

Sample for Salmonella paratyphi

1. Samples are taken like typhoid fever.
   1. Blood complete examination.
   2. Stool for culture.
   3. Blood for culture.
   4. Urine for culture.
2. Roughly 10⁵ to 10⁹ organisms are required for the culture, but this count may be low in infants and older adults.
3. This count may be low in patients taking antacids and H₂ receptor blockers.

Definition of Salmonella paratyphi

1. Salmonellae are flagellate, gram-negative bacteria that cause a self-limited disease that is food-borne and water-borne gastroenteritis or may cause life-threatening systemic disease caused by S. Typhi (Enteric fever or Typhoid fever).
   1. Salmonella paratyphi causes a less severe disease than Salmonella typhi.
2. Salmonella infections are divided into:
3. Typhoidal infection caused by S.typhi and S.paratyphi.
   1. Salmonella paratyphi is also a type of Enteric fever.
4. Non-typhoidal infection most common in the USA is caused by:
   1. 1. S. Typhimurium.
      2. S. enteritidis.
   2. 95% of cases are food-born, and the rest are nosocomial infections.
   3. Salmonella is relatively uncommon in the USA; 70% are acquired abroad.
   4. Humans are the only source of this infection, and the spread is from person to person or via contaminated foods or water.

Types of S. Paratyphi:

1. S. paratyphi A.
2. S. paratyphi B.
3. S. paratyphi C.

Pathogenesis of Salmonella paratyphi infection:

The incubation period

1. It is  6 to 30 days.
2. This is caused by Salmonella enterica, which has Paratyphi A, B, and C serotypes.

The spread of S. Paratyphi

1. It spreads through eating or drinking contaminated water or food from the patient’s feces or the carrier.
   1. Humans are the only animals infected.
   2. Occasionally this may spread sexually.
   3. Most cases are due to Paratyphi A compared to Paratyphi B and C.

Epidemiology of S. Paratyphi

1. Paratyphi B is more common in Europe.
   1. This will have S/S like typhoid fever.
   2. Diagnosis by isolating the bacteria or antibodies (anti-BH) in the widal test.
2. Paratyphi C is a rare infection mostly seen in the Far East.
   1. It presents as septicemia with the formation of an abscess.
   2. Culture usually makes the diagnosis.
   3. S. Paratyphi A and C are mostly seen in tropical countries.

Microbiology of S. Paratyphi

1. It is a gram-negative, flagellated bacteria.
2. Its growth is seen on special media:

Type of the media	Appearance in the media
MacConkey	Non-lactose fermenting, pale colonies
Desoxycholate citrate agar	Non-lactose fermenting, pale colonies
XLD agar	Red colonies with a black center. S. Paratyphi A is H2S negative, so there is no black center
Wilson and Blair bismuth sulfite agar	Shiny black metallic colonies
Tetrathionate broth and Selenite F	Growth shifted to selective media

3. Special test:
   1. S. Paratyphi does not produce gas during the fermentation of sugars.
   2. Serological identification done with salmonella polyvalent O and H-antisera.
   3. Bacteriophage study can differentiate S. Paratyphi B.

Pathogenesis of S. Paratyphi

1. These bacterias are internalized by the intestinal epithelial cells present over Peyer’s patches and are abundant in the ileum.
2. These are transported to the peyer patches; these bacteria enter the blood circulation from there.
3. S. Typhi often settles in the liver and biliary tree.
   

   Salmonella Paratyphi infection pathogenesis

Signs and symptoms of paratyphoid fever

1. These are like typhoid fever.
2. S/S are milder than typhoid fever.
   1. There are weaknesses and loss of appetite.
   2. Headache is quite common.
   3. Some patients may develop skin rashes that are rose-colored.
   4. Only 20% to 40% of the patient develops abdominal pain.
3. The duration is shorter.
4. There may be transient diarrhea and symptomless infection.
5. Without treatment, S/S may persist for weeks or months.

• Carrier state is less common.

Lab Diagnosis

1. CBC shows:
   1. Low TLC, leucopenia.
   2. 4000 to 6000/cmm during the first 2 weeks, and then 3000 to 5000/cmm during the next 2 weeks.
   3. Count >10,000/cmm indicates perforation or suppuration.
   4. Initially, there is normocytic anemia, and in case of bleeding as a complication, anemia becomes hypochromic and microcytic.
2. Blood culture:  This is the gold standard for the diagnosis.
   1. 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.
   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.
3. Bone marrow culture, if taken, will be positive and may have a high yield of up to 90% sensitivity.
4. 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 (another reference says after the 10th day), with increasing frequency up to 4th or 5th week in <50% of the cases.
      1. Stool culture after the 4 months indicates carrier state, which may be seen in ∼3% of the cases.
   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’s medium shows non-fermenting colonies.
      3. There is no gas and no fermentation of sugar.
5. The widal test
   1. The classical Widal test is difficult to interpret when patients have already been vaccinated.
   2.  IT will be positive after 7 to 10 days of infection.
   3. An agglutination test is done for flagellar H and somatic O antigen with antisera (Salmonella paratyphi A and B).

1. Widal test is not used in the routine because of:
   1. The widal test is positive in vaccinated cases.
   2. It is positive in the previous history of infection.
   3. Non-specific diseases may cause an increase in the titer.
   4. Autoimmune disease may see false-positive results.
   5. Early treatment of typhoid fever may give negative or low widal titers.
2. Typhidot test claimed by the manufacturing companies that it would be positive after 2 to 3 days.
   

   Interpretation of the Typhidot test in enteric fever

3. The urine culture may be done and is positive in the case of enteric fever but is less sensitive.
   1. This is done on the MacConkey media.
   2. Urine culture is positive during the 2nd to 3rd week in 25% of the patients, even if blood culture is negative.
4. Bacteriophage typing is done to identify the different strains of S. Typhi and Paratyphi.
   1. This is useful for the epidemiological investigation in case of the outbreak’s source.
5. Identification of S. paratyphi:
   1. Biochemical tests like there are no gas formation in the sugar fermentation.
   2. Blood culture and a urine culture can also identify these organisms.
   3. Serology shows H and O antisera positive tests.
   4. Bacteriophage typing identifies the different types of salmonella paratyphi.
      

      Type of salmonella	Motility	Indol/Urease	Lysine decarboxylase	Gas production
      Salmonella Paratyphi A	Positive	Negative	Negative	Positive
      Salmonella Paratyphi B	Positive	Negative	Positive	Positive
      Salmonella Paratyphi C	Positive	Negative	Positive	Positive

Treatment of Salmonella paratyphi

1. Ciprofloxacin and Co-trimoxazole can be given.
2. The drug of choice is chloramphenicol but not used because of its complication.
3. Treatment of carrier:
   1. The chronic carrier is less common but can be treated by ampicillin, chloramphenicol, ciprofloxacin.
   2. Ultimately can advise cholecystectomy.

Control: The following methods will help to prevent the spread of disease.

1. Public health, including general hygiene, should be discussed with the public.
2. The carrier should not be employed in the food industry. They should be taught public hygiene like washing hands and clean water supply,
3. Vaccination will also help to decrease the incidence of the disease.

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