SALMONELLA TYPHI IGG (TYPHIDOT) - SERUM

Salmonella Typhi IgG (Typhidot) – Serum

The Salmonella Typhi IgG (Typhidot) Test is a rapid serological blood test that detects IgG antibodies against antigens of Salmonella enterica serovar Typhi, the bacterium responsible for typhoid fever.

Typhoid fever, also known as enteric fever, is generally transmitted through food or water contaminated with human faeces. The infection may cause prolonged fever, headache, weakness, abdominal discomfort, loss of appetite, diarrhoea or constipation. Severe untreated infection can lead to intestinal bleeding, perforation, encephalopathy and other complications.

The Typhidot method commonly detects antibodies directed against a specific outer-membrane protein of Salmonella Typhi. Earlier studies described Typhidot as a rapid test capable of separately identifying IgM and IgG antibody responses. However, subsequent evaluations have shown variable accuracy across patient populations and geographic settings.

What Does Salmonella Typhi IgG Indicate?

IgG antibodies usually appear later than IgM antibodies and may remain detectable after the infection has resolved. Therefore:

• Positive IgG may indicate previous exposure, a later stage of infection or persistent antibodies from an earlier episode.
• Negative IgG means detectable antibodies were not found, but it does not exclude early typhoid fever.
• A positive IgG result does not prove active typhoid infection.

Typhoid serological tests cannot reliably distinguish an active infection from previous infection or vaccination. They may also show cross-reactivity and false-positive results, especially in areas where typhoid is common. CDC guidance therefore identifies blood culture as the preferred diagnostic method for acute typhoid fever.

Test Purpose

The test may help:

• Detect IgG antibodies associated with exposure to Salmonella Typhi.
• Support evaluation of patients with symptoms suggestive of enteric fever.
• Provide supplementary information when culture results are unavailable.
• Assess a possible later-stage or previous typhoid infection.
• Complement clinical examination and other laboratory investigations.

Benefits of the Test

• Requires only a small blood sample.
• Produces results rapidly.
• Detects the IgG antibody response separately.
• May provide supportive evidence of exposure.
• Useful as an adjunct where immediate culture facilities are limited.
• Can be performed without fasting.

Why Doctors May Recommend It

A doctor may request this test for a patient with persistent fever, headache, abdominal pain, diarrhoea, constipation, loss of appetite or a history of consuming potentially contaminated food or water.

It may be ordered with:

• Blood culture
• Complete blood count
• Liver function tests
• Stool culture
• Urine culture
• C-reactive protein
• Salmonella Typhi IgM
• Other investigations for prolonged fever

Because Typhidot accuracy varies, antibiotic treatment should not be started or continued solely because of an isolated IgG-positive result. Clinical evaluation and culture testing are important, particularly because antimicrobial resistance in Salmonella Typhi affects treatment selection.

Preparation Before the Test

No fasting or special preparation is generally required.

Inform the healthcare provider about:

• Duration of fever
• Previous typhoid infection
• Recent typhoid vaccination
• Current or recent antibiotic use
• Recent travel
• Consumption of unsafe food or water
• Previous blood-culture results
• Other current infections

A venous blood sample is collected, and serum is separated for the rapid immunoassay.

Reporting Time

Typically: 15–30 minutes after sample processing

Actual report delivery may vary depending on laboratory workflow and whether additional tests are requested.

Who Should Take This Test?

The test may be advised for:

• Patients with persistent or unexplained fever
• Individuals with suspected enteric fever
• Patients with abdominal symptoms and prolonged fever
• People exposed to unsafe food or water
• Travellers returning from typhoid-endemic regions
• Patients with inconclusive initial investigations
• Individuals undergoing a prolonged-fever evaluation
• Patients who cannot immediately undergo culture testing
• Individuals requiring supportive serological evaluation
• Anyone advised by a qualified healthcare professional