eMedicine Specialties > Pediatrics: General Medicine > Infectious Disease
Salmonella Infection
Updated: Jan 9, 2009
Introduction
Background
Infections due to Salmonella species represent a major public health problem in many countries. In the United States, nontyphoidal Salmonella (NTS) is the most common pathogen implicated in food-borne gastroenteritis. In most cases, NTS is a self-limiting disease that causes mild gastroenteritis; however, it can lead to a wide spectrum of complications including bacteremia, enterocolitis, and severe local infections such as meningitis and osteomyelitis. Salmonella serotype typhi can cause serious and prolonged bacteremic illness referred to as enteric fever or typhoid fever.1
Pathophysiology
The extension of the disease to various organs depends on the serotype, the size of the inoculum, and the status of the host. If large enough numbers of bacteria are ingested, they can survive in the normally lethal acidic pH of the stomach.Once ingested, Salmonella can gain access to the small intestine, producing diffuse mucosal inflammation, edema, and microabscesses. Generally, most NTS do not extend beyond the lamina propria and lymphatics of the gut. Exceptions include Salmonella choleraesuis and Salmonella dublin, which can cause bacteremia with little intestinal involvement.2 In individuals with S typhi, areas of intestinal necrosis can ulcerate and result in perforation. In addition, this mucosal penetration allows uptake into the draining lymph nodes, contributing to blood stream infections (BSI) and subsequent invasion of the liver, spleen, and bone marrow. This process explains the delayed onset of symptoms in S typhi.3
Frequency
United States
From 1996-2006, more than 50,000 laboratory-confirmed cases of NTS infections occurred annually, an average of 14.7 infections per 100,000 persons per year.4,5 Approximately 400 cases of typhoid fever are reported per year. More than two thirds of cases are acquired from foreign travel. From 1985-1994, travel to Mexico and India accounted for most cases of typhoid fever. However, in the last 10 years US travelers to Asia, Africa, and Latin America have been especially at risk.6
International
The past 2 decades have seen an increase in the incidence of NTS in Europe and North America.4 Typhoid fever is endemic in many developing areas of the world. Five Asian countries are considered to be endemic for typhoid: China, India, Indonesia, Pakistan, and Vietnam.1 Annually, the World Health Organization (WHO) estimates 16-33 million cases of typhoid fever worldwide and 500,000-600,000 deaths.
Mortality/Morbidity
Enteric infections account for significant morbidity and mortality in young children (aged 1-4 y). Morbidity and mortality rates are highest in infants (most dangerous in infants <3 mo with bacteremia), elderly patients, and patients with sickle cell disease, acquired immunodeficiency syndrome (AIDS), neoplasms, or other immunosuppressive conditions.1,7 Substantial differences in outcomes have been noted based on varying serotypes.5
Race
The incidence of infection for all serotyped NTS is almost twice as high in blacks and Latinos, Salmonella typhimurium is the most common pathogen.8
Sex
No sex differences are noted.8
Age
Attack rates are highest in persons younger than 5 years or older than 70 years.8,1
Clinical
History
Carefully obtain the patient's history to determine any potential sources of Salmonella and to help determine if the correct diagnosis has been made.
- General history
- Inquire about any recent travel abroad.
- Inquire about possible animal exposures, including contact with pet iguanas, turtles, tortoises, or other reptiles.
- Inquire whether any family members have current or recent gastroenteritis.
- Inquire whether any recent outbreaks have occurred in the community.
- Salmonella gastroenteritis
- The incubation period of Salmonella gastroenteritis is 6-72 hours.
- In most cases, children have cramping abdominal pain, nausea, vomiting, and loose watery stools.
- Stools may be bloody; however, this is not as common as in infection with Shigella.
- Fever, which rarely exceeds 39°C, occurs in approximately one half of infected patients.
- Symptoms usually resolve spontaneously in 2-7 days.
- Enteric fever (typhoid fever)
- Enteric fever is caused by S typhi and several other Salmonella serotypes.
- The incubation period for enteric fever is 3-60 days, but symptoms typically occur in 1-2 weeks.
- Patients may present with high fever, which rises in a steplike fashion.
- Other symptoms include anorexia, abdominal pain, malaise, myalgias, headache, cough, diarrhea or constipation, and delirium.
Physical
- Salmonella gastroenteritis
- Upon physical examination, patients may have signs of dehydration, such as delayed capillary refill, sunken eyes, dry mucous membranes, or tachycardia.
- Patients may have tenderness to palpation on abdominal examination, which sometimes can be difficult to differentiate from appendicitis.
- Rectal examination may reveal heme-positive stools, gross blood, or mucoid stools.
- Enteric fever (typhoid fever)
- A typical finding of enteric fever is relative bradycardia for the height of the fever.
- Hepatosplenomegaly may be found on examination.
- Patients with enteric fever may develop rose spots; these spots are blanching pink papules most commonly found on the anterior thorax. They usually fade about 3-4 days after appearance, are 2-4 mm in diameter, and occur in groups of 5-20.
Causes
- Salmonella organisms are gram-negative rod-shaped bacilli in the family Enterobacteriaceae. All Salmonella organisms are to be considered a single species (Salmonella enterica) because of their close relationship by DNA hybridization studies.3
- Differences in lipopolysaccharide (LPS) and flagellar structure generate the antigenic variation that is reflected in the more than 2500 known serotypes that cause human disease.
- Nontyphoidal Salmonella (NTS) serotypes are divided into O-antigen groups A through E. Since 1997, Salmonella enteritidis (D), S typhimurium (B), and Salmonella newport (C2) account for about half of the culture-confirmed Salmonella isolates.
- The principal reservoirs for NTS organisms are poultry, livestock, reptiles, and pets. The mode of transmission is ingestion of foods of animal origin, including poultry, red meats, unpasteurized milk, and eggs that have been contaminated by infected animals or an infected human.1
- Recent Salmonella outbreaks have been attributed to commercially produced items, such as peanut butter, frozen pot pies, puffed vegetable snacks, and dry dog food.9,10,11,12,13 Contact with infected reptiles, such as iguanas, pet turtles, and tortoises, and ingestion of contaminated water are other modes of transmission.
- S typhi (D) is the species known to cause enteric fever (typhoid fever). S typhi is found only in humans. In the United States, typhoid fever is usually caused by foreign travel to countries with contaminated food and drinking water or by ingestion of food contaminated by a chronic carrier.1 Travelers visiting friends and relatives in typhoid-endemic countries may be at more risk than tourists because of a lack of precautionary measures.14 Historically, Salmonella paratyphi (A) has been the cause of a smaller proportion of the cases of enteric fever. However, China and India are experiencing a substantial increase in enteric fever caused by S paratyphi (A).15
- Recently, excess antibiotic use in the prior year has been associated with a higher incidence of NTS. Disruption of the microflora of the gut has been offered as a possible cause; however, an alternate explanation may be that these individuals are a more medically fragile group, requiring more antibiotics and, in general, are more susceptible to illness.16
More on Salmonella Infection |
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| Differential Diagnoses & Workup: Salmonella Infection |
| Treatment & Medication: Salmonella Infection |
| Follow-up: Salmonella Infection |
| References |
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Further Reading
Keywords
Salmonella infection, bacterial gastroenteritis, infectious colitis, Salmonella typhi, S typhi, enteric fever, typhoid fever, Salmonella enteritidis, S enteritidis, nontyphoidal Salmonella, NTS, bacteremia, meningitis, food-borne gastroenteritis, osteomyelitis, cell disease, AIDS, neoplasms, appendicitis, hepatosplenomegaly, bradycardia
