Salmonella Infection

Dr. Rathivika sundar, MBBS, MRCP (UK) fellowship in infectious diseases

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What is Salmonella? 

Salmonella is a group of bacteria known to cause infection primarily in the gastrointestinal system. The disease is called Salmonellosis or, in common terms, Salmonella poisoning. These are rod-shaped and Gram-negative bacteria. Important bacteria belonging to the Salmonella group are the Salmonella typhii and Salmonella paratyphii causing Typhoid and Para-typhoid fevers, respectively. These are also known as Enteric fever. 

Salmonellosis is caused by contaminated food or water from an infected person or carrier. A carrier is a person who has the bacteria and is able to spread the infection but does not show symptoms and remains undiagnosed. Such persons can carry and spread the organism for many years. 

Common food sources of Salmonella are: (Journal of global health, 2012, June)

• Raw or under-cooked meat and eggs
• Unpasteurized milk and milk products such as cheese, butter, yoghurt, ice cream
• Raw fruits and vegetables that have been sprayed or washed with contaminated water

The commonest symptoms of Salmonellosis are fever, cramp-like pain in the abdomen, nausea, loose stools and vomiting. These may or may not be accompanied by Myalgia and Malaise. The incubation period is the time interval between the causative microbe entering the body and the development of the first symptom. The incubation period for Salmonella is 6 hours to 6 days, but this can vary depending on various factors. 

Can Salmonella kill you?

If untreated, the mortality rate of Typhoid is 10-30%, which reduces to 1-4% in those receiving treatment. Typhoid fever is caused by Salmonella typhii. The symptoms are similar to those mentioned above, but typhoid also causes systemic symptoms. It can spread through blood and affect the lungs, brain, spinal cord, heart, liver, bone and joints. Typhoid can cause ulceration in the intestines which can cause complications such as intestinal Haemorrhage and perforation.

To diagnose Typhoid, the following investigations are used:

• Culture of the bacteria from blood, bone marrow, occasionally stool sample
• Blood level of immunoglobulin, IgM and IgG against Typhoid 
• Serial WIDAL test 
• Other general blood investigations generally show a lymphocyte predominance and no increase in the WBC count. 

Certain characteristic features of typhoid fever are:

• Relative Bradycardia: Usually, there is an increase in the heart rate with an increase in the body temperature (during fever). This does not occur in Typhoid fever.
• Rose spots: These appear after 2 to 3 weeks of the disease. Rose spots are red to the pinkish flat rash seen over the neck, chest and abdomen. 
• Very high temperatures, about 103-104 F (39-40 C)

Treatment for Typhoid is by taking the prescribed course of antibiotics. There is a lot of emerging antibiotic resistance for Typhoid; hence the type of antibiotic used for treatment may vary. The antibiotics are given for a prolonged duration to prevent relapse. In some people, Typhoid can relapse about 1 week after completing the antibiotic course. The blood cultures may become positive again, and the patients start showing similar symptoms. Typhoid relapse needs to be treated on a case-to-case basis. 

Prevention of Salmonella related diseases are the following:

• Frequent handwashing with soap and water, especially before eating or handling food and after using the toilet.
• Drink clean water. Water that is boiled and cooled or RO/UV treated water. 
• Avoid consuming raw fruits and vegetables from restaurants. Avoid salads, fruits juices, etc.
• Wash raw fruits and vegetables thoroughly with clean water before consuming.
• Consume cooked and hot food if dining at restaurants.

Vaccination against Typhoid 

There are two types of vaccines available:

1. Inactivated (killed) Typhoid vaccine: In the form of intramuscular injection. A booster dose may be required every 2 years.
2. Live attenuated (weakened) Typhoid vaccine: A dose of 4 capsules taken orally on alternate days. A booster dose may be required every 5 years. (cdc.gov, centre for disease control and prevention)

Conclusion

Salmonella continues to be an infective disease causing significant strain on the healthcare system of developing countries, especially south-east Asian countries. Health awareness, improvement in hygiene and availability of healthcare resources is necessary to reduce this burden.