Paratyphoid fever

Unique identifier / Notation

BI0225

Synonyms

Enteric fever

Paratyphoid fever results from systemic infection with Salmonella enterica serotype Paratyphi. It is characterised by febrile illness and, in severe cases, gastrointestinal bleeding, altered mental status, intestinal perforation, and death (IHME 2021).

Primary reference(s)

Institute for Health Metrics and Evaluation (IHME), 2021. Global Burden of Disease Cause and Risk Summary: Paratyphoid fever. Seattle, USA: IHME, University of Washington, 2021. Accessed 26 May 2025.

Annotations

Additional scientific description

Paratyphoid fever (together with typhoid fever, collectively known as enteric fever) is caused by Salmonella enterica serovars Paratyphi (S. Paratyphi) A, B and C. S (WHO, 2022).

Paratyphi A is the most common serovar while Paratyphi C is uncommon. S. Paratyphi A, like S. Typhi, has adapted to human hosts; it causes similar clinical syndromes to typhoid, including fevers, chills, and abdominal pain, and can be a life-threatening illness in severe cases (WHO, 2022).

Incidence rates of paratyphoid fever vary widely according to geography; it is most prevalent in South and South East Asia but is not as common in Africa. Incidence is highest among children, peaking in the 5-9-year age group. Age-specific incidence may vary by country, and children with paratyphoid are generally older than those with typhoid (WHO, 2022).

S. Paratyphi infection is primarily treated with fluoroquinolones, third-generation cephalosporins, and azithromycin. Antimicrobial resistance (AMR) remains a major threat, including the potential for extreme drug resistance and azithromycin resistance. Carbapenems are reserved for suspected infection with extensively drug-resistant strains (WHO, 2022).

Humans are the only source of these bacteria; no animal or environmental reservoirs have been identified (CDC, 2024). The onset of illness is insidious, with gradually increasing fatigue and a fever that increases daily from low-grade to high (CDC, 2024). Headache, malaise, and anorexia are nearly universal, and abdominal pain, diarrhoea, or constipation are common (CDC, 2024). Paratyphoid fever appears to have a lower case-fatality ratio than typhoid fever; however, severe cases do occur (CDC, 2024).

Blood culture is the mainstay of diagnosis in typhoid and paratyphoid fever. Bone marrow and stool cultures can also be used (Gupta et al., 2008; CDC, 2024).

Metrics and numeric limits

The Global Burden of Disease (GBD) study 2019 estimated 3.8 million cases of paratyphoid fever (due predominantly to paratyphoid A) and 23,300 deaths globally, and an age-standardized incidence of 51.3/100,000.

2·17 million (95% UI 1·56-2·96) cases of paratyphoid fever occurred in 2021, resulting in 14,300 deaths (6,000-28,900) and 1·01 million (0·457-2·00) DALYs (IHME, 2021).

Key relevant UN convention / multilateral treaty

International Health Regulations (2005), 3rd ed. (WHO, 2016).

Drivers

Paratyphoid fever is acquired through consumption of water or food contaminated by faeces of an acutely infected or convalescent person, or a person with chronic, asymptomatic carriage (CDC, 2024).

Impacts

Paratyphoid fever is estimated to be responsible for approximately one-fifth of all enteric fever cases, but its overall relative burden compared to typhoid fever is highly variable depending on the geographic context and is reportedly increasing. There are observations that the increase may be associated with vaccination against typhoid, thus it is important to monitor the burden of paratyphoid fever, especially with the implementation of typhoid conjugate vaccines (Sundeep et al., 2008; WHO, 2022).

Multi-hazard context

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 (CDC, 2024).

Risk Management

Antibiotic therapy shortens the clinical course of enteric fever and reduces the risk of death. Treatment decisions are complicated by high rates of resistance to many antimicrobial agents, and antimicrobial treatment should be guided by susceptibility testing. A careful travel history can inform empiric treatment choices while awaiting culture results (CDC, 2024). Relapse, reinfection, and chronic carriage also can occur. Relapse occurs in ≤10% of patients 1–3 weeks after clinical recovery, requiring further antibiotic treatment. An estimated 1%–4% of treated patients become asymptomatic chronic carriers (defined as people who excrete the organism in stool for ≥12 months); a prolonged antibiotic course is usually required to eradicate the organism (CDC, 2024). Safe food and water precautions and frequent handwashing (especially before meals) are important preventative measures. available for paratyphoid fever; thus, food and water precautions are the only prevention methods (CDC, 2024).

Monitoring

WHO supports countries to conduct all-hazards strategic risk assessment in the contexts of health emergencies and disasters, which results in the development of a country risk profile. Empowered with the country risk profile, inclusive of a seasonal risk calendar, countries can anticipate potential emergencies before they occur to trigger early alerts and inform early actions (WHO, 2021).

WHO's Early Warning, Alert and Response System (EWARS) has been designed to improve disease outbreak detection in emergency settings, such as in countries in conflict or following a natural disaster. It is a simple and cost-effective way to rapidly set up a disease surveillance system. EWARS is deployed during an emergency as an adjunct to the national disease surveillance system. WHO works with Ministries of Health and health sector partners to train local health workers to use the system. After the emergency, EWARS should re-integrate back into the national system (WHO, no date).