Non-Typhoidal Salmonella
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Direct answer
Non-typhoidal Salmonella serotypes, mainly Salmonella Typhimurium and Salmonella Enteritidis, cause self-limiting gastroenteritis after ingestion of contaminated food, eggs or poultry. In infants, older adults, people with HIV and those with sickle cell disease, the organisms can invade the bloodstream or bone and cause bacteraemia or osteomyelitis. Routine antibiotics are not needed for uncomplicated gastroenteritis in healthy people.
What you must remember
- Common serotypes: Salmonella Typhimurium and Salmonella Enteritidis are frequent causes of gastroenteritis, acquired from poultry, eggs and other animal products.
- Zoonotic reservoir: unlike Salmonella Typhi, non-typhoidal serotypes live in animals as well as humans and lack a Vi capsule.
- Clinical picture: diarrhoea, abdominal cramps and fever that usually settle within a few days in healthy hosts.
- Invasive risk: bacteraemia is more likely in infants, older adults, people with HIV, malaria and immunosuppression.
- Sickle cell disease: functional asplenia impairs clearance of bloodstream bacteria, and Salmonella osteomyelitis is a classic complication, often of long bones.
- Prolonged carriage: faecal shedding can persist for weeks to months after an acute infection.
- Laboratory: non-lactose-fermenting, motile and hydrogen sulphide-producing, forming red colonies with black centres on XLD agar.
A stepwise approach to suspected invasive Salmonella infection
A 3-year-old with sickle cell disease has fever, diarrhoea and a painful, swollen femur. The steps show how invasive disease is recognised and managed.
- Confirm with stool culture: culture on selective media such as XLD or Salmonella-Shigella agar confirms the organism and allows susceptibility testing.
- Take blood cultures when invasive: fever, toxicity or immunocompromise call for blood culture before antibiotics, because bacteraemia is more common in these groups.
- Assess for focal infection: bone pain, joint swelling, meningitis or endovascular infection should prompt imaging, and osteomyelitis in sickle cell disease is a classic presentation.
- Rehydrate and support: oral rehydration is the mainstay for gastroenteritis, and intravenous fluids are needed for severe dehydration.
- Choose antibiotics by susceptibility: ceftriaxone or azithromycin is commonly used for invasive disease, and courses are extended for osteomyelitis and immunocompromised patients.
- Consider surgery for bone infection: debridement or drainage may be needed alongside prolonged antibiotics when bone infection is established.
Where the exam tries to catch you
Non-typhoidal Salmonella questions test whether the student separates routine gastroenteritis from invasive disease and remembers the high-risk hosts.
- Trap: giving antibiotics for every case of Salmonella gastroenteritis Correct: routine treatment is not needed in healthy hosts, and antibiotics may prolong faecal carriage.
- Trap: assuming non-typhoidal Salmonella causes enteric fever Correct: it causes gastroenteritis and invasive bacteraemia, while enteric fever is the systemic syndrome caused by Salmonella Typhi and Paratyphi.
- Trap: forgetting sickle cell disease in a child with Salmonella bone infection Correct: Salmonella osteomyelitis is a classic association with sickle cell disease, so haemoglobinopathy must be considered in the history.
Frequently asked questions
Which serotypes of non-typhoidal Salmonella cause most gastroenteritis?
Salmonella Typhimurium and Salmonella Enteritidis are among the most common non-typhoidal serotypes causing gastroenteritis. They are usually acquired through contaminated food, including poultry, eggs and other animal products.
Why does sickle cell disease predispose to non-typhoidal Salmonella bacteraemia?
Functional asplenia in sickle cell disease impairs clearance of bloodstream bacteria, so non-typhoidal Salmonella bacteraemia and osteomyelitis are recognised complications. Bone infarction is also thought to create a site where Salmonella can seed.
Does uncomplicated non-typhoidal Salmonella gastroenteritis need antibiotics?
Uncomplicated non-typhoidal Salmonella gastroenteritis in healthy people usually resolves without antibiotics, and oral rehydration is the mainstay of treatment. Antibiotics are reserved for invasive disease, bacteraemia and immunocompromised patients.
How does non-typhoidal Salmonella differ from Salmonella Typhi in laboratory tests?
Non-typhoidal serotypes typically produce hydrogen sulphide and form red colonies with black centres on XLD agar. Salmonella Typhi usually produces little or no hydrogen sulphide, and it is Vi-positive, which distinguishes it from the non-typhoidal serotypes.
Why is Salmonella osteomyelitis common in children with sickle cell disease?
Salmonella osteomyelitis is a classic complication in children with sickle cell disease, often affecting long bones such as the femur. Bacteraemia can seed bone, and infarcted marrow is thought to predispose to infection, so bone pain with fever needs prompt evaluation.