Salmonella refers to bacteria belonging to the genus Salmonella, a group of Gram-negative, usually motile, facultatively anaerobic organisms within the Enterobacterales. Human disease is broadly divided into non-typhoidal Salmonella infections and enteric fever caused by Salmonella enterica serovars Typhi and Paratyphi. Non-typhoidal infections commonly cause acute gastroenteritis, while typhoid and paratyphoid fever can produce systemic illness. The term therefore encompasses organisms and clinical syndromes that differ substantially in epidemiology and pathogenesis. Salmonella can infect humans and numerous animal hosts, making food production, animal reservoirs and food handling important components of its transmission ecology.
Non-typhoidal Salmonella is commonly transmitted through contaminated food or water and through contact with infected animals or their environments. Common sources can include undercooked eggs, poultry, meat and other contaminated foods, although virtually any food can become contaminated. Cross-contamination during food preparation can transfer organisms from raw products to ready-to-eat foods. Person-to-person transmission can occur through faecal-oral spread, particularly where hygiene is inadequate. Reptiles and some other animals can carry Salmonella without appearing ill, making hand hygiene after animal contact important.
Salmonella gastroenteritis typically causes diarrhoea, abdominal cramps, fever, nausea and sometimes vomiting. Symptoms often develop after an incubation period of several hours to several days, depending on dose and host factors. Most uncomplicated infections are self-limited, but dehydration can become clinically significant, particularly in young children, older adults and people with certain underlying conditions. Salmonella can occasionally invade beyond the intestine and produce bacteraemia or focal infections such as osteomyelitis. The risk of invasive disease is greater in people with impaired immunity and some other medical risk factors.
Enteric fever caused by S. Typhi and S. Paratyphi differs from typical non-typhoidal gastroenteritis. These organisms are adapted primarily to humans and can cross the intestinal barrier, survive within macrophages and disseminate through the reticuloendothelial system. Typhoid fever can cause prolonged fever, headache, abdominal symptoms and systemic illness, with serious complications including intestinal perforation, gastrointestinal bleeding and encephalopathy in severe cases. Chronic carriage can occur, with organisms persisting in the biliary system and being shed intermittently. The epidemiology of enteric fever is strongly associated with sanitation, water quality and food hygiene.
Laboratory diagnosis generally relies on culture of stool or, for invasive disease and enteric fever, blood or other relevant specimens. Culture provides an isolate that can be identified and tested for antimicrobial susceptibility. Molecular methods can also detect bacterial genetic material and may be useful for rapid diagnosis, although culture remains important for surveillance and resistance analysis. A positive stool test does not necessarily distinguish asymptomatic carriage from disease in every circumstance, so results must be interpreted in relation to symptoms. In suspected enteric fever, blood culture is particularly important because the organism may not be reliably identified through routine stool testing early in illness.
Treatment of uncomplicated non-typhoidal Salmonella gastroenteritis often consists primarily of fluid and electrolyte replacement because many cases resolve without antibiotics. Antibiotics may be considered for severe disease or people at increased risk of invasive infection, with decisions guided by clinical circumstances and resistance patterns. In enteric fever, effective antibiotics are essential, but increasing antimicrobial resistance has complicated treatment in many regions. Inappropriate antibiotic use can also have disadvantages, including disruption of the intestinal microbiome and selection for resistant organisms. Treatment should therefore be based on current clinical guidance and, when possible, susceptibility information.
Prevention of Salmonella depends on food safety, sanitation, hand hygiene and appropriate cooking and storage. Thorough cooking can destroy bacteria, while preventing cross-contamination reduces transfer to ready-to-eat foods. Eggs, poultry and other high-risk foods require appropriate handling, and refrigeration slows bacterial multiplication but does not necessarily kill organisms. Vaccines are available for typhoid fever and are particularly relevant for people living in or travelling to areas where typhoid is endemic, although typhoid vaccines do not provide universal protection and do not prevent ordinary non-typhoidal Salmonella gastroenteritis.
Salmonella should not be treated as a single disease because non-typhoidal gastroenteritis and enteric fever differ in reservoirs, transmission, clinical course and treatment. The term “food poisoning” is also broader than Salmonella and includes numerous bacterial, viral and toxin-mediated illnesses. Salmonella has major public-health importance because it can move through complex food-production systems and can acquire antimicrobial resistance. Effective control therefore involves surveillance, agricultural and food-industry measures, household hygiene, clinical management and public-health investigation rather than relying solely on treatment after illness occurs.
