Salmonella

Salmonella enterica is a Gram-negative, facultative anaerobic, intracellular bacillus belonging to the Enterobacteriaceae family. It is widely distributed in nature and is a major cause of foodborne zoonotic infections in humans. More than 2,500 serotypes have been identified, with Salmonella Enteritidis and Salmonella Typhimurium being the most common in human infections. The species is divided into six subspecies, with S. enterica subsp. enterica being the most clinically relevant.

Clinical features:
Salmonella infections can be classified into three main syndromes: gastroenteritis, enteric fever (typhoid and paratyphoid fever), and focal systemic infections. The most common presentation is gastroenteritis, characterized by diarrhea, fever, abdominal pain, nausea, and occasionally vomiting. Symptoms typically appear between 6 and 72 hours after ingestion of contaminated food and usually resolve within 2 to 7 days. Most cases are self-limiting.

In approximately 5% of cases, particularly in immunocompromised individuals, infants, or the elderly, invasive disease can occur, presenting as bacteremia or secondary infections such as meningitis, pneumonia, osteomyelitis, endocarditis, or septic arthritis.

Typhoid fever, caused by Salmonella Typhi (which possesses a capsule), is a systemic illness marked by prolonged fever, malaise, relative bradycardia, hepatosplenomegaly, and sometimes rose spots on the trunk. Intestinal complications like hemorrhage or perforation may occur. This presentation is more common in developing regions with poor sanitation.

Salmonella may also cause urinary tract infections, cholecystitis, joint infections, or deep-tissue abscesses. In pregnancy, although the incidence is not increased, systemic dissemination can be associated with fetal complications.

Diagnosis:
Diagnosis is based on bacterial culture, particularly from stool samples in cases of gastroenteritis, or from blood, bone marrow, or other sterile body fluids in cases of enteric fever or systemic disease. Culture remains the gold standard, although nucleic acid amplification tests (NAATs) provide faster and more sensitive detection. Serotyping according to the Kauffmann-White scheme is important for epidemiological purposes.

Treatment:
Treatment of uncomplicated gastroenteritis is usually supportive, involving rehydration and electrolyte management. Antibiotics are reserved for severe, prolonged, or systemic cases or for patients at risk of complications. Commonly used agents include fluoroquinolones (e.g., ciprofloxacin), third-generation cephalosporins (e.g., ceftriaxone), and azithromycin. However, increasing antimicrobial resistance—especially among endemic strains—poses a growing therapeutic challenge.

In typhoid fever, early antibiotic treatment is critical and may require hospitalization. The emergence of multidrug-resistant Salmonella Typhi has led to the use of newer treatment regimens and the need for ongoing epidemiological surveillance.

Salmonella remains a significant public health concern due to its high prevalence, foodborne transmission potential, and ability to cause outbreaks. Prevention relies on food hygiene, animal health control, and proper cooking practices.