Salmonella Infections

Salmonella is a motile, nonencapsulated gram-negative bacillus within the Enterobacteriaceae family. Salmonella enterica is the species that causes the vast majority of human infections. It is further divided into more than 2500 serovars, notably including nontyphoidal salmonellae (NTS) and S. enterica subtype typhi. These organisms are responsible for a range of clinical syndromes.NTS is a leading cause of foodborne infections worldwide, with gastroenteritis being the most common presentation, particularly among children in the first 5 years of life. According to the Centers for Disease Control and Prevention (CDC), NTS accounts for an estimated 1.35 million illnesses and 420 deaths annually in the United States.Conversely, typhoid fever, predominantly caused by S. enterica subtype typhi, is most prevalent in South and Southeast Asia, where it remains a significant health burden, causing more than half a million deaths annually. The CDC estimates that 620 hospitalizations and 5700 illnesses from typhoid fever occur annually in the United States, with the majority of infections occurring in individuals who traveled to endemic regions.Salmonella is recognized as a leading cause of foodborne illness in the United States, primarily transmitted through contaminated food products. It has been linked to numerous outbreaks documented by the CDC over the past decade, with implicated sources including eggs, fresh produce, peanut butter, and flour.In addition to foodborne transmission, contact with reptiles such as turtles, snakes, lizards, and iguanas poses a risk for salmonella infection. These animals can carry the bacteria in their intestinal tracts, leading to human exposure through direct or indirect contact. Following infection with NTS, the bacteria are excreted in feces for a median duration of 5 weeks. However, in children aged younger than 5 years, the excretion period may extend up to 20 weeks, increasing the potential for transmission to others.A chronic asymptomatic carrier state with Salmonella typhi is possible and primarily occurs in adults—these individuals represent an important epidemiological reservoir of the organism, with exposure to chronic carriers accounting for approximately 30% of new typhoid fever infections in the United States.NTS presentation can vary from asymptomatic to serious illnesses, such as bacteremia, meningitis, brain abscesses, and osteomyelitis. The most common presentation is gastroenteritis, usually within 12 to 96 hours after ingestion of contaminated food or water. Symptoms may include diarrhea (can be bloody depending on causative serotype), nausea, vomiting, abdominal cramps, and fever. Patients may also have nonspecific symptoms such as headache, fatigue, and chills. The illness is usually self-limited, with diarrhea typically ending within 7 days.Complications such as bacteremia are rare. However, in up to 10% of patients with bacteremia, extraintestinal focal infections such as abscesses and osteomyelitis can occur. In children aged younger than 1 year, salmonella meningitis can occur as a rare form of invasive disease. In general, risk factors for invasive disease include age younger than 12 months, patients with sickle cell disease, severe malnutrition, and immunosuppressed patients.In typhoid fever, typical symptoms seen in children include gradual onset of fever with abdominal pain, anorexia, malaise, headache, and cough. Examination findings can include hepatosplenomegaly, dactylitis, and rose spots (slightly raised blanching, erythematous lesions that can be difficult to appreciate in dark-skinned individuals). Later complications include shock and gastrointestinal bleeding. In younger children and infants, the presentation can vary from mild febrile illness to bacteremia to meningitis.Diagnosis of NTS is made by isolating salmonella from stool, blood, or urine cultures or from another site of infection, including cerebrospinal fluid, bronchoalveolar lavage fluid, and pleural fluid. Stool testing (cultures or polymerase chain reaction [PCR]–based assays) should be obtained when children present with bloody, persistent, or severe diarrhea. Although stool PCR testing is available for salmonella, culture is still important in terms of determining antimicrobial susceptibility when treatment is indicated. Testing can be useful from a public health perspective in terms of control of spread.Blood cultures should be obtained in patients who will require treatment for NTS disease, including infants aged younger than 3 months and immunocompromised children. In children with unexplained fever after travel to typhoid endemic areas (including Eastern and Southern Asia, Africa, Central and South America, and the Middle East), blood and stool cultures should be obtained. To diagnose typhoid fever, several cultures might be necessary. Diagnosis is usually made from blood, bone marrow, or bile cultures because the organism is not usually found in stool early in the illness.Uncomplicated gastroenteritis from NTS is treated with supportive measures such as rehydration and replacement of electrolyte losses, similar to other types of infectious gastroenteritis. Oral rehydration is first line, but more severe dehydration may require nasogastric or intravenous fluids. Symptomatic treatment with antidiarrheal agents such as loperamide should be avoided in children due to potential adverse effects such as ileus and possible worse outcomes from certain pathogens. An antiemetic such as ondansetron may be considered to assist with oral rehydration and decrease losses due to vomiting. Although they are used widely, antiemetics are not recommended for routine treatment of gastroenteritis as they can lead to increased stool losses. Patients can continue a regular diet as tolerated.Antibiotic treatment for NTS gastrointestinal illness is not routinely recommended. It has not been shown to shorten duration of symptoms and can prolong fecal shedding and increase risk of relapse. Antibiotics are recommended for those at risk for invasive disease, including infants aged younger than 3 months and patients with underlying medical conditions such as hemoglobinopathies, immunocompromised states, and existing gastrointestinal disorders such as inflammatory bowel diseases. Antibiotic therapy can be considered in otherwise healthy patients who have more severe disease. If antibiotics are indicated, a stool and blood culture should be collected before giving a dose of ceftriaxone. Azithromycin is an oral option once the patient is stable for outpatient management. Ampicillin/amoxicillin, trimethoprim-sulfamethoxazole, and fluoroquinolones are other options depending on sensitivity results.More serious infections from NTS such as bacteremia, meningitis, and osteomyelitis all require parenteral antibiotic therapy of varying durations regardless of age or underlying conditions. Ceftriaxone is the initial therapy for these infections as well. Following initiation of antibiotic therapy for NTS bacteremia, serial blood cultures should be obtained until clearance is documented.In contrast to NTS, all typhoid infections need antibiotics because they shorten the duration of symptoms and decrease mortality. Initial antibiotic choice is dependent on travel history because resistance varies regionally. It is important to access up-to-date information regarding local resistance patterns. Patients may also need supportive care such as antipyretics and rehydration. Infectious disease specialists should be consulted for patients with any severe or invasive forms of NTS and for all cases of typhoid fever.Hand hygiene, as well as food, water, and pet safety measures, are important for the prevention of salmonella infections. Specific risks include handling of reptiles, amphibians, and live poultry as well as the consumption of raw eggs and unpasteurized milk. This is especially true for patients who are at risk for invasive disease.For NTS infections, exclusion from childcare or school settings is only needed if stools are not contained in a diaper for infants/toddlers or if an older child or adult is incontinent of stool or still has an excess of 2 stools more than their usual pattern.All salmonella infections should be reported to the health department in most states. For typhoid infections, the health department should additionally be consulted to determine when testing is needed and how long the patient should be excluded from group settings, as this will vary based on location. In general, negative stool samples will be needed once antibiotic therapy is complete before return.Immunization is only available for people at risk for Salmonella typhi infection. A live attenuated oral vaccine is available to those aged 6 years and older and a polysaccharide injectable vaccine is available to people aged 2 years and older. In the United States, the main group of people eligible for typhoid vaccine are travelers to high-risk areas. Obtaining comprehensive travel plans from patients traveling outside the United States is important for assessing risk of typhoid exposure and facilitates the provision of necessary vaccinations and guidance on food and water safety.When I was in medical school, I took care of a patient with sickle cell disease who presented with recurrent infections with salmonella. Upon further questioning, our team discovered this school-aged boy had a lizard for a pet. Although this is now a well-recognized risk factor, at that time, I found it amazing that a careful history including types of pets in the household and knowledge about exposure to certain animals was critical in minimizing risks to patients who had hemoglobinopathies or immunocompromised conditions. I remember how difficult it was to convince him and his family to find another home for the pet lizard, yet the relocation of the lizard to another household resulted in a safer environment for my patient, who had no further salmonella infections.Being knowledgeable about salmonella outbreaks is an important public health measure and beneficial for our patients. On Red Book: Online Outbreaks Red Book Online Outbreaks | Red Book Online | American Academy of Pediatrics (aap.org), there were several mentions of recent outbreaks from salmonella infections including exposure in certain locations to cucumber, fresh basil, and also backyard poultry. This online website remains a good resource for all clinicians and our patients.Janet Serwint, MDAssociate Editor, In Brief