Investigations
1st investigations to order
stool studies
Test
Stool studies, either by isolating the organism from fresh stool samples sent for culture or by detection of specific DNA in faeces, are the only way to make the diagnosis of Salmonella gastroenteritis.
Stool collected by the patient is the recommended sample. Cultures using rectal swabs are less sensitive and are not recommended (unless a stool culture cannot be obtained).[44]
Stool samples are directly plated on enteric media (e.g., MacConkey agar) or more selective media for Salmonella (e.g., Hektoen agar). Highly selective media (e.g., selenite with brilliant green) are typically reserved for known carriers, or for use during outbreak investigations.[45]
Many laboratories use incubation in an enrichment broth such as Selenite-F to increase the sensitivity of the stool culture.
Guidelines recommend stool culture studies if the patient has moderate to severe disease with symptoms lasting more than 7 days, or diarrhoea accompanied by fever, bloody or mucoid stools, severe abdominal cramping or tenderness, or signs of sepsis.[66][68]
Stool testing should also be performed in symptomatic patients who have clearly identified circumstances in which Salmonella infection is suspected: foodborne outbreaks in hotels, cruise ships, resorts, restaurants, institutions, and catered events; consumption of unpasteurised milk or dairy products; consumption of fruits or unpasteurised fruit juices, vegetables, leafy greens, and sprouts; consumption of undercooked eggs; swimming in or drinking untreated fresh water; recent antimicrobial therapy; travel to resource-challenged countries; contact with young poultry or reptiles; patient is an infant (birth to 3 months of age), or an adult >50 years or with a history of atherosclerosis; patient has an underlying immunocompromising condition; anal-genital, oral-anal, or digital-anal contact.[66]
Salmonella may also be diagnosed from stool using a multiplex polymerase chain reaction (PCR) panel with primers for several common diarrhoeal pathogens. This technique is highly sensitive and specific.[69][70]
Multiplex PCR panels are increasingly used for the evaluation of patients with acute infectious gastroenteritis, due to their superior sensitivity and shorter turnaround time.[71][79] Reflexive culture should be performed whenever Salmonella (or Shigella or Campylobacter) are detected, in order to provide isolates for susceptibility testing and strain typing.[72][73]
Result
growth of Salmonella on selective media or detection of specific DNA in faeces
Investigations to consider
blood cultures
Test
Should be obtained from symptomatic patients: <3 months of age; with signs of septicaemia or when enteric fever is suspected; with systemic manifestations of infection; who are immunocompromised; with high-risk conditions such as haemolytic anaemia; who have travelled to or have had contact with travellers from enteric, fever-endemic areas with febrile illness of unknown aetiology.[66]
Result
may be positive for Salmonella
imaging studies
Test
Imaging studies (e.g., ultrasonography, computed tomography, or magnetic resonance imaging) are not routine. However, they may be considered to detect aortitis, mycotic aneurysms, signs and symptoms of peritonitis, intra-abdominal free air, toxic megacolon, or extravascular foci of infection in older people with invasive Salmonella enterica infection if there is sustained fever or bacteraemia, despite adequate antimicrobial therapy, or if the patient has underlying atherosclerosis or has recent-onset chest, back, or abdominal pain.[66]
Result
may detect aortitis, mycotic aneurysms, signs and symptoms of peritonitis, intra-abdominal free air, toxic megacolon, or extravascular foci of infection
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