Typhoid fever

Typhoid fever, also known as typhoid, is a disease caused by Salmonella serotype Typhi bacteria.[2] Symptoms may vary from mild to severe, and usually begin 6 to 30 days after exposure.[3][4] Often there is a gradual onset of a high fever over several days.[3] This is commonly accompanied by weakness, abdominal pain, constipation, headaches, and mild vomiting.[4][5] Some people develop a skin rash with rose colored spots.[4] In severe cases, people may experience confusion.[5] Without treatment, symptoms may last weeks or months.[4] Diarrhea is uncommon.[5] Other people may carry the bacterium without being affected, but they are still able to spread the disease to others.[6] Typhoid fever is a type of enteric fever, along with paratyphoid fever.[2] So far, S. enterica Typhi is only known to infect and replicate within humans.[7]

Typhoid Fever
Other namesEnteric Fever, slow fever
Causative agent: Salmonella enterica serological variant Typhi (shown under a microscope with flagellar stain)
SpecialtyInfectious disease 
SymptomsFever that starts low and increases daily, possibly reaching as high as 104.9 F (40.5 C) Headache, Weakness and fatigue, Muscle aches, Sweating, Dry cough, Loss of appetite and weight loss, Stomach pain, Diarrhea or constipation, Rash, Swollen stomach (enlarged liver or spleen)
Usual onset1-2 weeks after ingestion
DurationUsually 7-10 days after antibiotic treatment begins. Longer if there are complications or drug resistance
CausesGastrointestinal infection of Salmonella enterica serovar Typhi
Risk factorsWork in or travel to areas where typhoid fever is established, Work as a clinical microbiologist handling Salmonella typhi bacteria, Have close contact with someone who is infected or has recently been infected with typhoid fever, Drink water polluted by sewage that contains Salmonella typhi
PreventionPreventable by vaccine. Travelers to regions with higher typhoid prevalence are usually encouraged to get a vaccination before travel.
TreatmentAntibiotics, hydration, surgery in extreme cases. Quarantine to avoid exposing others (not commonly done in modern times)
PrognosisLikely to recover without complications if proper antibiotics administered and diagnosed early. If infecting strain is multi-drug resistant or extensively drug resistant then prognosis more difficult to determine.

Among untreated acute cases, 10% will shed bacteria for three months after initial onset of symptoms, and 2-5% will become chronic typhoid carriers.[1]

Some carriers are diagnosed by positive tissue specimen. Chronic carriers are by definition asymptomatic.[1]

The cause is the bacterium Salmonella enterica subsp. enterica serovar Typhi growing in the intestines, peyers patches, mesenteric lymph nodes, spleen, liver, gallbladder, bone marrow and blood.[4][5] Typhoid is spread by eating or drinking food or water contaminated with the feces from an infected person.[6] Risk factors include limited access to clean drinking water, and poor sanitation.[2] Those who have not yet been exposed to the pathogen and ingest contaminated drinking water or food are most at risk for developing symptoms.[5] As far as we currently know, only humans can be infected; there are no known animal reservoirs.[6] Diagnosis is by culturing and identifying the Salmonella enterica Typhi bacterium from patient samples or detecting an immune response to the pathogen from blood samples.[4][2][8] Recently, new advances in large-scale data collection and analysis are allowing researchers to develop better diagnostics - such as detecting changing abundances of small molecules in the blood that may specifically indicate typhoid fever.[9] Diagnostic tools in regions where typhoid is most prevalent are quite limited in terms of accuracy and specificity; the time required for a proper diagnosis, increasing spread of antibiotic resistance, and the cost of testing is also a concern for under-resourced healthcare systems.[7]

A typhoid vaccine can prevent about 40 to 90% of cases during the first two years.[10] The vaccine may have some effect for up to seven years.[2] For those at high risk or people traveling to areas where the disease is common, vaccination is recommended.[6] Other efforts to prevent the disease include providing clean drinking water, good sanitation, and handwashing.[4][6] Until an individual's infection is confirmed as cleared, the individual should not prepare food for others.[4] The disease is treated with antibiotics such as azithromycin, fluoroquinolones, or third-generation cephalosporins.[2] Resistance to these antibiotics has been developing, which has made treatment of the disease more difficult.[2][11]

In 2015, 12.5 million new cases worldwide were reported.[12] The disease is most common in India.[2] Children are most commonly affected.[2][6] Rates of disease decreased in the developed world in the 1940s as a result of improved sanitation and use of antibiotics to treat the disease.[6] Each year in the United States, about 400 cases are reported and the disease occurs in an estimated 6,000 people.[5][13] In 2015, it resulted in about 149,000 deaths worldwide – down from 181,000 in 1990 (about 0.3% of the global total).[14][15] The risk of death may be as high as 20% without treatment.[6] With treatment, it is between 1 and 4%.[2][6]

Typhus is a different disease.[16] Due to the similarity in symptoms, they were not recognized as distinct diseases until the 1800s. The name typhoid means "resembling typhus".[17]