Enteric fever – Part 3 – Typhoid / Enteric fever Diagnosis, Widal test, Its Procedure and Interpretation

Sample

1. It is done on the serum of the patient.
2. A random sample can be taken.

Purpose of the test (Indication)

• This test is done to diagnose enteric fever (Typhoid and paratyphoid fever).

pathophysiology

1. History of widal test:
   1. In 1896 widal test was discovered by George-Fernand Widal for the diagnosis of enteric fever.
2. Enteric fever includes typhoid and paratyphoid fever.
   1. Paratyphoid fever is milder than typhoid fever.
   2. Enteric fever is also called typhoid fever.
3. Typhoid fever is caused by the bacterium Salmonella Typhi.
   1. Salmonella typhi has an incubation period of 14 to 21 days. Sometimes may even longer.
   2. 30% of the cases become chronic carriers due to persistent infection of the gallbladder.
4. This has flagellar antigen H antigen, and Lipopolysaccharides antigen is somatic or O antigen.
   

   Typhoid bacilli structure

3. The incubation period is 7 to 14 days.
4. Typhoid fever is common in the developing world, where it affects about 21.5 million persons each year.
5. Salmonella Typhi lives in humans and is also found in chickens and eggs.
6. It is present in the blood and intestinal tract.
7. The carrier can harbor bacilli in the gallbladder.
8. Both patients and carriers shed Salmonella Typhi in their feces (stool).

Mode of spread

1. Food: if food or drinks are contaminated.
2. Spread from the carrier, who is shedding Salmonella Typhi.
3. Contaminated drinking water: If sewage water is contaminated with Salmonella Typhi.
4. Typhoid fever is more common in areas of the world where handwashing is less frequent.
5. Once Salmonella Typhi bacteria are eaten or drunk, they multiply and spread into the bloodstream.

Signs and symptoms

1. The patient has a fever, and the pattern of the fever is typical.
2. Fever is persistent and does not touch normally. This may be as high as 103 to 104 F.
3. The patient may feel weak.
4. May have stomach pains, headaches, or loss of appetite.
5. In some cases, patients have a rash of flat type and rose-colored spots.

The procedure of the Widal test:

1. Serial dilution of the patient serum is taken 1:40 to 1:320
2. Now add an equal volume of Salmonella antigen.
3. This can be done as a Slide method or as a Tube method.
4. When running in the tube, then incubate tubes for 12 hours or overnight.
5. Prepare the serial dilution, as shown in the diagram.
   

   Widal test procedure and dilution

Widal test procedure:

It is done as follows and can read the result where there is the start of the agglutination, as shown in the following diagram.

Drawback: This test will be positive after 7 to 10 days of Enteric fever.

1. 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.
   2. Widal test will be positive after 7 to 10 days of infection.
   3. The titer of O-antibodies 1:80 is suspicious in unvaccinated patients.
   4. The titer of 1:160 is strongly suggestive of infection in unvaccinated individuals.
   5. The titer of 1:40 for Antibody to flagellar-antigen (H) are suspicious in unvaccinated individual.
      1. While 1:160 is strongly suggestive.
   6. Titers are much higher in the vaccinated individual.
   7. Vi antigen for S.typhi is used to screen the carrier. antibodies to Vi-antigen are positive in

Reading of the test

1. The highest dilution of the serum is noted where there is agglutination.
2. If it ends at 1:320, then that is the titer.
3. The Widal test is positive
   1. if “O” antigen titer is    >1:160 = active infection.
   2. If the “H” antigen titer is     >1:160, it indicates past infection or in immunized persons.
   3. A fourfold increase in the titer (e.g., from 1:40 to 1:160) is diagnostic.

O antigen

1. In the acute stage, Antigen O will be positive, and titer will be more than 1:160.
2. O antigen appears early and also disappear early.

H antigen

1. H antigen rises late and disappears late.
2. This will be positive in the recovery stage.

Vi antigen

1. This is an indicator of the carrier stage.

The false-positive test may be seen due to cross-reacting infections, including malaria.

Other diagnostic tests for the diagnosis of Typhoid (Enteric) fever are:

1. Blood culture, which will be positive in the first week when the Widal test is negative.
2. Stool culture.
   1. 60 to 70% of cases are negative during the first week, and more cases positive in the third week of infection.
   2. Stool 90% of the cases are cleared of the bacteria by the 8th week of infection.
3. Urine culture.
4. Bone marrow culture. This is a very sensitive test.
   1. Bone marrow 90% of the cases are positive despite antibiotic therapy if these are ≤5 days.
5. Another serological test is Typhidot.
   1. The gold standard is the blood culture, where 90% of cases are positive in the first week.
   2. 50% of cases are positive by the third week.
   3. For better yield, centrifuge the blood and take a buffy coat for culture.
6. Other samples are stool, urine, Rose spot, bone marrow, and gastric or intestinal secretions.
7. When culture is done simultaneously on blood, bone marrow, and intestinal secretions, positivity is >90%.
8. A small % become the carrier, and their stool culture remains positive for at least one year.
   

   Enteric fever diagnosis

Culture in Enteric fever patients from  a different site:

Time period	Clinical S/S	Blood	Stool	Urine	Bone marrow
During I.P 0 to 1 week	diarrhea or constipation	negative	±	negative	negative
1 to 2 weeks	fever, headache, myalgia, cough	80 to 90% positive	negative	negative	negative
2 to 4 weeks	systemic toxemia	80 to 90% positive	80% positive	25% positive	90% positive
4 to 5 weeks	recovering	negative except in complications	50% positive	10% positive	±
>5 weeks	Cholecystitis, osteomyelitis	negative except in complications	±	±	negative

Treatment

1. The drug of choice is chloramphenicol, but it has many side-effects.
2. Ciprofloxacin is now a drug of choice.
3. Ampicillin, amoxicillin, 3rd generation cephalosporins, and fluoroquinolones can be used.
4. C0-trimoxazole is better than chloramphenicol with less side-effect.

Carriers:

1. 1. It is difficult to treat carriers because of gall bladder involvement.
   2. Ampicillin is the most useful drug, but it is to be given in larger doses and for a longer period of time.
   3. Chloramphenicol is less effective than ampicillin.
   4. Ciprofloxacin can also be tried.
   5. The ultimate end is cholecystectomy.

For Nonmedical (non-specialists) person explanation of Widal test (Enteric fever):

1. Please advise the Widal test if the fever persists for more than 5 days and is constant. It does not touch the normal level.
2. The titer of O antigen 1:40 is considered negative.
3. Just see the O antigen titer if it is 1:160, indicate Enteric fever.
4. If the O antigen is 1:80, repeat the test after 5 to 7 days, and now if the titer is 1:160, the rising titer again indicates acute infection.
5. While H antigen does not indicate acute infection or acute enteric fever.