What is the Salmonella paratyphi test?

The Salmonella paratyphi test works with a variety of culture specimens including faecal, serum, plasma and whole blood culture. This test utilises O and H antigens from both Salmonella typhi and Salmonella paratyphi antigens to maximise test sensitivity. It also distinguishes between IgG and IgM antibodies to determine the stage of paratyphoid infection. The test also provides a broader detection capability of Salmonella paratyphi A.

Paratyphoid fever usually develops in 1-2 weeks of exposure and varies in severity. Symptoms are very similar to other common infections and they include high fever, weakness, lethargy, muscle pain, headache, loss of appetite and diarrhoea or constipation. Hence the Salmonella paratyphi test is needed for confirmation of a paratyphi infection.

The test strip has: 

1) A coloured conjugate pad containing monoclonal anti Salmonella typhi/paratyphi conjugated with colloidal gold (anti- Salmonella typhi/paratyphi conjugates) 

2) A nitrocellulose membrane strip having two test lines (P and T line) plus a control line (C line). The P line is pre-coated with monoclonal anti- Salmonella paratyphi, the T line is pre-coated with monoclonal anti- Salmonella typhi, and the C line is pre-coated with a control line antibody. 

When a sufficient amount of specimen or faecal sample is properly distributed into the sample well of the test cassette, the specimen moves by capillary action across the cassette. If present in the specimen, the Salmonella paratyphi antigen will bind to the anti-Salmonella paratyphi conjugate. The immune-complex is then captured on the membrane by the pre-coated antibody forming a coloured P line, indicating a positive test result. 

The absence of test lines (P and T lines) is suggestive of a negative result. The C line should exhibit a coloured line of the immune-complex of the control antibodies, regardless of the colour development on the T or P line. Otherwise the test results are false and the specimen must be retested with another device.

Salmonella paratyphi or paratyphoid fever is a bacterial infection caused due to the subspecies of a bacteria called Salmonella enterica growing in a person’s intestines and blood. Symptoms are usually seen 6-28 days after exposure including the gradual onset of high-grade fever.

Salmonella is a broad group of bacterial species out of which the subspecies named Salmonella enterica contains a huge number of pathogenic serotypes including those causing both typhoid and paratyphoid fevers, which can infect a broad range of hosts.

Antibiotic treatment is generally preferred for treating paratyphi infections. Deaths are very rare and people suffering from paratyphi infections are usually given antibiotics, which start showing results within 2 to 3 days. Resistance to antibiotics is gradually increasing; hence taking care to prevent infections always remains important. Plenty of fluids are also advised to counter dehydration caused by fever and diarrhoea.

Paratyphoid fever usually spreads by eating or drinking food or water contaminated with the faecal matter of an infected person or through the preparation of food by an infected person. 

Since paratyphi infections are generally seen among poor, crowded populations, inadequate sanitation is a prime risk factor. The chronic stage may follow an acute illness or even mild or subclinical infections.

Paratyphoid fever is clinically very similar and almost indistinguishable from that of typhoid fever. The major difference perceived can be the shorter incubation period, comparatively milder symptoms, faster recovery time and fewer complications of paratyphoid fever. Thus, the Salmonella paratyphi test is a must to identify paratyphoid fever.

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