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Mahesh

10/05/24 14:52 PM IST

Widal test

In News
  • More often than not, the experience for patients with a fever is to get tested and treated for a typhoid infection.
  • The test is a rapid blood test called the Widal test.
About Typhoid
  • Typhoid spreads through contaminated food and water and is caused by Salmonella typhiand other related bacteria.
  • Also known as enteric fever, it presents with a high fever, stomach pain, weakness, and other symptoms like nausea, vomiting, diarrhoea or constipation, and a rash.
  • Some people, called carriers, may remain symptom-free and shed the bacteria in their stool for several months to years.
  • These symptoms mimic those of malaria, dengue, influenza, and typhus, to name a few, each with different treatment modalities.
  • If left untreated, typhoid can be life-threatening.
  • Per the World Health Organisation, 90 lakh people are diagnosed worldwide with typhoid every year and 1.1 lakh die of it.
  • A small 2023 study reported the burden to be 576-1173 cases per 100,000 child-years (one child year is one child being followed up for one year) in urban areas and 35 per 100,000 child years in rural Pune.
Diagnosis of Typhoid
  • The gold standard for diagnosing typhoid — in addition to a detailed medical history and a thorough examination — is to isolate the bacteria from a patient’s blood or bone marrow and grow them in the lab.
  • Stool and urine samples can also yield the same but with lower sensitivity.
  • However, performing culture tests in smaller clinical settings presents practical problems.
  • Cultures are time-consuming and skill- and resource-intensive.
  • Prior antibiotic treatment can also affect the results of cultures — a common issue due to the indiscriminate use of antibiotics in India.
  • Some PCR-based molecular methods are known to be better but are limited by cost; the need for specialised infrastructure and skilled personnel; and the inability to retrieve live bacteria for further tests.
  • Against this backdrop, in India, clinicians use the Widal test extensively to diagnose typhoid in both public and private sectors.
  • As with other infections, our immune system produces antibodies in the blood against the bacteria, causing enteric fever.
  • The Widal test rapidly detects and quantifies these antibodies. It’s a point-of-care test and doesn’t need special skills or infrastructure.
  • Developed in the late 1800s by a French physician, it is no longer used in many countries because of its flaws — flaws that are rendered by the scale of the test’s use in India to be abusive.
Appropriateness of Test
  • A single positive Widal test report doesn’t necessarily mean a typhoid infection is present, and a negative report doesn’t confirm the disease’s absence.
  • To diagnose an active infection, clinicians must test at least two serum samples taken at least 7-14 days apart, so that they may detect a change in concentrations of the antibodies.
  • But getting two samples is rarely feasible and time-consuming.
  • Second, in areas with high and continuous typhoid burden, certain levels of antibodies against the bacteria may already be present in the blood.
  • Without knowing the baseline cut-off, it isn’t possible to correctly interpret the test.
  • A related issue is that different manufacturers of the test specify different cut-off values in their kits’ user manuals.
  • Third, the reagents used in the Widal test to reveal the presence of various antibodies can cross-react with antibodies produced against infections by other bacteria, viruses or parasites, or even in typhoid-vaccinated individuals, leading to false positives.
  • Prior antibiotic therapy can also affect antibody levels and yield a false negative.
  • Correct diagnosis and appropriate treatment of enteric fever are important because serious complications, like severe intestinal bleeding or perforation, can develop within a few weeks if the disease is mismanaged. False negatives can thus delay diagnosis and lead to fatal outcomes.
Source- The Hindu

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