How the Widal test is clouding India’s sense of its typhoid problem | Explained Premium

Because of the Widal test’s propensity for erroneous results, the actual burden of typhoid in India remains obfuscated.

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. The subsequent treatment usually consists of tablets, typically in urban areas, or injections in rural ones.

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.

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.