Typhoid fever, also called enteric fever, is a life-threatening infection caused by the bacterium Salmonella. It is a serious health threat, especially for children, in places where it is more common. It is usually spread through contaminated food or water. An estimated 11–21 million cases of typhoid fever occur worldwide each year, with a mortality rate of 1–4%. Once Salmonella Typhi bacteria are ingested, they multiply and spread into the bloodstream.
Survival
It's possible for the bacteria to live in the body for 12 months or more after infection. Typhoid fever lasts seven to 10 days when treated soon after symptoms start. If untreated or if treatment starts later, it can last three weeks or longer. If you have complications or a relapse, it can take longer than that to fully recover. It may be needed to have a further 28-day course of antibiotics to "flush out" the bacteria. Until test results show that the individual is free of bacteria, it is recommended to avoid handling or preparing food.
The bacteria can survive several weeks in dry environments and several months in wet environments. Salmonella can survive for up to 4 weeks on dry surfaces in high-enough populations to be transferred to foods and can be transferred to the foods almost immediately on contact. The ability of bacteria to survive and cross-contaminate other foods even after long periods of time on dry surfaces, thus reinforcing the importance of sanitation on food contact to minimize the risk of foodborne illness.
Transmission
Typhoid fever is acquired through consumption of water or food contaminated by feces of an acutely infected or convalescent person, or a person with chronic, asymptomatic carriage. Typhoid bacilli are shed in stool of asymptomatic carriers or in stool or urine of people with active disease.
Risk for infection is high in low- and middle-income countries with endemic disease and poor access to safe food and water, and poor sanitation. Sexual contact, particularly among men who have sex with men, has been documented as a rare route of transmission.
Inadequate hygiene after defecation may spread Typhoid bacteria to community food or water supplies. In endemic areas where sanitary measures are generally inadequate, Typhoid bacteria are transmitted more frequently by water than by food. In areas where sanitary measures are generally adequate, transmission is chiefly by food that has been contaminated during preparation by healthy carriers.
Amongst food items, ice and unbranded ice cream have been implicated as vehicles of the infectious agent. Food contamination in turn can occur through water or by food handlers who may be carriers. Unsterile eating utensils, like knives and forks, can also cause typhoid if cleaned in unsanitary water.
Sporadic typhoid cases may be observed round-the-year that are mainly attributed to intermittent mixing of underground sewerage and drinking water due to damaged pipelines. Overcrowding has also been implicated in the transmission of the organism.
It is now almost universally admitted that the common house fly, and perhaps other flies, play a certain part in the transmission of typhoid fever.
It is believed that the cockroach may be a reservoir for a range of bacteria including salmonella. Cockroaches accumulate this disease by consuming feces contaminated with the bacterium.
Rarely, hospital personnel who have not taken adequate enteric precautions have acquired the disease when changing soiled bedclothes.
Who is Most at Risk?
An episode of typhoid fever usually means that the individual lives in an environment in which further exposure to infection is likely.
Typhoid risk is higher in populations that lack access to safe water and adequate sanitation, and children are at highest risk. Travellers to areas of the world where the cause of the illness is common are at the highest risk. Travellers do not have the same immunity to local bacteria as the people who live there. This increases the risk of food and water-borne diseases like typhoid fever for travellers.
The risk is usually low in areas with access to clean water, safe food-handling practices, higher standards of cleanliness and accommodation, and proper sewage (human waste) disposal.
Gastric Acidity
Ingestion of large numbers of Typhoid bacteria is necessary to overcome gastric acidity. Generally, the infective dose of enteric pathogens is related to a number of factors, including their ability to cope with acid. The infective dose of Salmonella is about one million pathogens.
It is reasonable to assume that the temporary increase in pH following consumption of food may help Salmonella to survive the harsh stomach conditions. In addition, it has been suggested that certain solid food sources, especially those rich in fat or with a high protein content, protect Salmonella against stomach acidity, and feed composition has been shown to influence the gastric pH and the stomach organic acid content. With regard to liquid foods, such as water and juices, their short emptying time from the stomach could also facilitate Salmonella survival.
Low gastric acidity, which is common among older people and among people who use acid-suppressing drugs, can markedly decrease the infective dose.
Immunity
An attack of typhoid fever does not provide long lasting immunity from a future episode of the same illness. People can be reinfected if they come into contact with the bacteria again. People with weakened immune systems (reduced ability to fight disease) are at higher risk of severe illness from typhoid fever.
Typhoid vaccines lose effectiveness over time. The injectable vaccine requires a booster every 2 years, and the oral vaccine requires a booster every 5 years.
Genes are linked to humans' ability to resist typhoid fever. It was found that carrying a particular form of the HLA-DRB1 gene provides natural resistance against typhoid. The HLA molecules are in general very important because they are able to recognize invading bacteria and turn on the body's immune system.
Clinical Presentation
The duration of the typhoid illness is about 3-4 weeks. The onset of illness is insidious, with gradually increasing fatigue and a fever that increases daily from low-grade to 38°C–40°C by the third or fourth day of illness. Fever is commonly lowest in the morning, peaking in the late afternoon or evening. Anorexia, headache, and malaise are nearly universal, and abdominal pain, constipation, or diarrhea are common. Diarrhea and vomiting are more common in children than in adults. People also can have dry cough, fatigue, myalgias, and sore throat. Hepatosplenomegaly often can be detected. A transient, maculopapular rash of rose-colored spots can occasionally be seen on the trunk.
The clinical presentation is often confused with malaria. We suspect enteric fever in a person with a history of travel to an endemic area who is not responding to antimalarial medication. Untreated, the disease can last for a month, and reported case-fatality ratios are 10%–30%. By comparison, the case-fatality ratio in patients treated early is usually <1%.
Serious complications of typhoid fever occur in 10%–15% of hospitalized patients, generally after 2–3 weeks of illness, and include life-threatening gastrointestinal hemorrhage, intestinal perforation, and encephalopathy.
Can Typhoid be Resistant?
A growing threat. Multidrug-resistant (MDR) typhoid, defined as resistance to three first-line antibiotics used to treat typhoid—chloramphenicol, ampicillin, and cotrimoxazole— first appeared in the 1970s and has since spread globally.
Salmonella Carrier State
A chronic carrier state occurs in 1-4% of patients with untreated typhoid Salmonella. Chronic enteric carriers harbor organisms in their gallbladder and shed them in stool for > 1 year. Some carriers have no history of clinical illness. Most human typhoid convalescents continue to shed S. Typhi in feces for <4 weeks. Long-term persistent carriers may last for decades.
Most Chronic enteric carriers harbor infection in their gallbladders wherein preexisting pathologies, particularly cholelithiasis, provide an environment that fosters persistence. They are asymptomatic carriers, and they excrete large numbers of the bacteria in their feces and transmit the pathogen by contaminating water or food sources.
Prevention
Countries with less access to clean water and washing facilities typically have a higher number of typhoid cases.
Wash hands after using the bathroom and changing diapers, and before handling or eating any food. Make sure that persons with diarrhea, especially children, wash their hands carefully and frequently with soap to reduce the risk of spreading the infection.
Keep raw meat and poultry separate from produce and other foods when shopping for and storing groceries. Wash hands, cutting boards, countertops, cutlery, and utensils after handling uncooked poultry. Wash raw fruits and vegetables before eating. Food and kitchen tools and surfaces may become contaminated from raw food products. Thoroughly cook raw meat and poultry to destroy the bacteria.
Defrost food in the refrigerator, in cold water, or in the microwave. Because salmonella bacteria grow and multiply at room temperature, foods should not be left out of the refrigerator for more than 2 hours.
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