bacillary dysentery

Last edited 04/2023 and last reviewed 05/2023

Bacillary dysentery is caused by Shigella, with Shigella sonnei responsible for more than 90% of cases in UK, but causing the mildest form of the condition, S. flexneri, S. boydii and S. dysenteriae causing progressively more severe dysentery.

The inoculating dose is small - about 200 organisms.

The organisms invade the superficial colonic mucosa causing inflammation. Local multiplication and invasion is possible via a virulence factor, together with the production of a toxin. A cholera-like presentation may occur if the disease is due to S. dysenteriae, which produces a cytotoxin, Shiga toxin. The shiga-like toxins are related, but less potent, and are produced by Shigella sp. and also by enterohaemorrhagic E. Coli.

Outbreaks occur in nurseries, mental and geriatric institutions - the latter two are on the decline - underlining the fact that the faecal-oral route is needed. Some 50% of cases occur in children less than 10 years old.

Summary:

Cause:

• 4 species of shigella: Shigella sonnei, Shigella flexneri, Shigella boydii, Shigella dysenteriae

Reservoir:

• Humans

Epidemiology:

• infections peak in late summer in the UK
• highest rates of infection occur in children aged < 5 years, followed by 5-14 year age group
• S. sonnei is the most common species in Western Europe and both S. sonnei and S. flexneri are endemic in UK
• most cases of S. boydii and S. dysenteriae are imported but all strains may be travel-associated

Transmission:

• faeco-oral transmission directly amongst households, nursery and infant schools is most common. Foodborne infections occur but are rare
• direct transmission between men-who-have-sex-with-men (MSM) is also an important transmission route
  • cases in males are often associated with sexual transmission via direct oral-anal contact, or oral sex after anal sex or play, including fingering or use of sex toys (2)
    • in 2019, 52% of adult cases were thought to be sexually transmitted among gay, bisexual, and other men who have sex with men (GBMSM)
• environmental contamination during episodes of acute diarrhoea can occur, where bacilli may be aerosolised during toilet flushing and settle on surrounding surfaces and survive for weeks in cool and humid locations

Incubation period:

• 12 hours - 4 days (usually 1-3 days) but up to 1 week for S. dysenteriae

Common clinical features:

• clinical features vary depending on Shigella species
• S. sonnei causes mild illness in most cases with symptoms of diarrhoea (may be bloody in 10-50%) and abdominal pain with/without nausea, vomiting, headache and malaise lasting average of 4-5 days (range 1 day – 2 weeks)
• S. flexneri causes similar symptoms to S. sonnei but illness may be more severe with dysentery more prominent, longer duration of illness and hospitalisation rates higher
• complications include reactive arthritis and Reiter’s syndrome
• S. boydii causes diarrhoeal illness like that of S. flexneri
• S. dysenteriae type 1 infection causes more severe illness, with dysentery in most cases and complications including haemolytic uraemic syndrome (HUS)

Infectivity:

• cases are most infectious when diarrhoea is present but considered infectious as long as organisms are excreted in stool (average of 2- 4 weeks but prolonged carriage of several months has been reported)

Management:

• seek expert microbiology advice
• antibiotic treatment is not required for all cases of shigellosis
• cases with prolonged symptoms or complications may require antibiotics
  • commonly used antibiotics include macrolides, fluoroquinolones, aminoglycosides, sulphonamides, trimethoprim, tetracycline, and third-generation cephalosporins
  • in the UK, note that the among GBMSM, the proportion of all Shigella spp. isolates that are multi-drug resistant, or XDR (extensively drug resistant) is very high, often exceeding 90% (2)

Notes:

• clinicians should specifically ask for travel and sexual history for those presenting with acute diarrhoeal illness, and request appropriate diagnostic tests, that is, faecal bacterial culture and polymerase chain reaction test (if available), and antibiotic susceptibility testing for Shigella spp., from adult males presenting with acute diarrhoea who have not travelled and identify as GBMSM (2)
• also recommended that stool samples be taken from those with prolonged diarrhoea (>7 days), blood in stools, and those with severe illness requiring hospitalisation (2)

Reference:

• PHE (2019). Recommendations for the Public Health Management of Gastrointestinal Infections
• Charles H et al. Spotlight on drug-resistant Shigella: raising awareness within general practice. BJGP 2023; 73 (729): 187-188. DOI: https://doi.org/10.3399/bjgp23X732537