Shigella infection (Shigellosis)

Queensland Health Guidelines for Public Health Units

Revision History

• Disclaimer
• Infectious Agent
• Notification Criteria
• Notification Procedure
• Reporting to NOCS
• Public Health Significance and Occurrence
• Clinical Features
• Reservoir
• Mode of Transmission
• Incubation Period
• Period of Communicability
• Susceptibility and Resistance
• Management
• Preventive Measures
• Summary
• References

Infectious Agent

The agent is the bacterium, Shigella.

There are four species or serogroups:
Group A  - S. dysenteriae
Group B - S. flexneri
Group C - S. boydii
Group D - S. sonnei

Groups A, B and C are further divided into different serotypes. Group D comprises a single serotype which can be further subdivided into five biotypes (a, b, e, f and g).

Notification Criteria

Laboratory Definitive Evidence:Isolation of Shigella species.

Laboratory Suggestive Evidence: Detection of Shigella by nucleic acid testing.

Epidemiological evidence: An epidemiological link is established when there is:

1. Contact with a confirmed case involving a plausible mode of transmission;
   

   OR

2. An epidemiologically plausible food or other environmental exposure in common with one or more culture-positive cases.

Confirmed case

A confirmed case requires

1. Laboratory definitive evidence.
   

   OR

2. Laboratory suggestive evidence AND epidemiological evidence.

Probable case

A probable case requires Laboratory suggestive evidence.

Community Outbreak Criteria:Two or more epidemiologically linked cases of the same serogroup.

Objectives of Surveillance:

* To monitor the epidemiology of shigellosis and to inform public health initiatives.
* To detect cases and outbreaks of disease, so as to enable prompt public health responses.

Notification Procedure

Pathology Laboratories:To notify on initial isolation and on microbiological confirmation by usual means.

Attending Medical Practitioners/Medical Superintendents (or Delegates):Notify two or more possibly linked cases of gastroenteritis by phone or facsimile.

Institutions (residential care facilities, hospitals):Notify two or more possibly linked cases of gastroenteritis by phone or facsimile.

Reporting to NOCS

Both confirmed cases and probable cases should be notified.

Public Health Significance and Occurrence

Shigellosis occurs worldwide. Two-thirds of the cases and most of the deaths are in children under 10 years of age. Illness in infants under 6 months of age is unusual. Outbreaks usually occur in conditions of crowding and where personal hygiene is poor, such as in prisons, institutions for children, childcare centres, psychiatric hospitals and crowded refugee camps. Outbreaks among men who have sex with men (MSM) have occurred in Queensland and elsewhere.¹

S. sonnei is the most common species in Queensland and the rest of Australia, comprising 75% of total Shigella notifications in Queensland from 2013-17*.  S. flexneri also occurs relatively commonly in Queensland, with S. boydii and S. dysenteriae more rarely seen, comprising 23%, 2% and <1% of total Shigella notifications in Queensland from 2013-17, respectively*. S. dysenteriae is considered the most virulent and has the potential to produce a potent cytotoxin known as “Shiga toxin”. It is often associated with serious disease and a high fatality rate, causing severe complications including haemolytic uraemic syndrome. S. sonnei is usually associated with a milder illness and short clinical course, whereas S. flexneri and S. boydii can cause either severe or mild illness.^1,2

*data extracted from Notifiable Conditions System (NoCS) Queensland (unpublished), Communicable Diseases Branch, Queensland Health (2013-2017)

Table 1. Comparison of Shigella species by severity of illness, occurrence of clinical features and sequelae

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Clinical Features

An acute bacterial disease involving the large and distal small intestine. It is characterised by diarrhoea which may contain blood or mucous (although many cases present with non-bloody diarrhoea), accompanied by fever, nausea and vomiting. Mild and asymptomatic infections occur. Illness is usually self-limited, lasting an average of 4–7 days. The severity of illness and the case-fatality rate are functions of the host (age, pre-existing state of nutrition and immune status) and the serotype.¹

Reservoir

Humans are the only significant reservoir.

Mode of Transmission

Mainly by direct or indirect faecal-oral transmission from an infected person or carrier. Infection may occur after the ingestion of contaminated food or water, as well as from person to person.^1,2 Some sexual practices, particularly between MSM, can increase risk of transmission. There are three high-risk groups in which Shigella infection occurs in Queensland; returned travellers; Indigenous communities; and MSM. Overcrowding and poor hygiene contribute to the burden of disease in Indigenous communities.

Incubation Period

From 12 to 96 hours (usually 1–3 days). Up to 1 week for S. dysenteriae 1.

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Period of Communicability

During acute infection and until the infectious agent is no longer present in faeces, as determined by negative culture, usually within 4 weeks after onset of illness. Asymptomatic carriers may transmit infection. Rarely, the carrier state may persist for months or longer. Appropriate antimicrobial treatment usually reduces duration of carriage to a few days.

Susceptibility and Resistance

Susceptibility is general, with infection following ingestion of very few (10–100) organisms. The disease is more severe in young children than in adults, among whom many infections may be asymptomatic. The elderly, the debilitated and the malnourished of all ages are particularly susceptible to severe disease and death. Breastfeeding is partially protective.¹

Management

Cases:

• Investigation:
  Investigate all confirmed cases. PHUs should follow up all cases, either by contacting GP or case to identify ‘high-risk’ situations, e.g. food handlers, attendance at childcare, childcare workers, healthcare workers or MSM. The case report form may be used to guide investigation.  Email completed case report forms to OzFoodNet (OzFoodNetQld@health.qld.gov.au) to facilitate identification of multi-jurisdictional clusters.
• Restriction:
  Exclude all cases from work, school or childcare until 48hrs after the diarrhoea has ceased (see table 2). For cases who are food handlers, work in child care, or are carers of  patients or the elderly, exclusion should continue until 48hrs after diarrhoea has ceased and one faecal culture or PCR^* has been negative (collected no sooner than 48hrs after discontinuance of antimicrobials). Isolate all cases occurring in residential care facilities until 48 hours after cessation of diarrhoea.

  All cases of S. dysenteriae regardless of risk group should be excluded 48hrs after diarrhoea has ceased and once one faecal culture or PCR has been negative (collected no sooner than 48hrs after discontinuance of antimicrobials).

  Regarding stool testing, evidence has shown that absence of Shigella species in the first convalescent faecal culture precludes a 100% probability of the second faecal culture being negative, thus one culture is considered adequate measure of clearance.⁵

  ^*PCR targeting the ipaH gene locus has been shown to be more sensitive than faecal culture at detecting presence of Shigella in stool^6,7,8

  Table 2. Recommended restriction for Shigella cases based on risk group and species

  Shigella species	Case is in a high-risk group (food handlers; carers of patients, children or the elderly) Yes                                                                No
  S. sonnei	1 negative clearance stool culture or PCR*	Exclusion for 48hrs after diarrhoea ceased
  S. flexneri	1 negative clearance stool culture or PCR*	Exclusion for 48hrs after diarrhoea ceased
  S. boydii	1 negative clearance stool culture or PCR*	Exclusion for 48hrs after diarrhoea ceased
  S. dysenteriae	1 negative clearance stool culture or PCR*	1 negative clearance stool culture or PCR*

  *taken 48hrs after diarrhoea has ceased and no sooner than 48hrs after finishing antibiotics.

• Treatment:
  Antibiotics shorten the duration and severity of illness and the duration of pathogen excretion. A systematic review of Shigella infection in children under 5 years of age found treatment with appropriate antibiotics provides successful clearance for 96% of cases.³ Furthermore, evidence from a 10-year Australian review found that the majority of Shigella cases have negative faecal cultures after appropriate antibiotics, with only 2.3% of cases having positive faecal cultures post antibiotics.⁴ For treatment regimens refer to the current edition of the Therapeutic Guidelines: Antibiotics. Antibiotics are used in individual cases based on the severity of the illness or to shorten the duration of the infective period and protect contacts (e.g. in childcare centres, residential care facilities or hospitals). Multidrug resistance to most of the low-cost antibiotics (ampicillin, trimethoprim-sulfamethoxazole) is common and the choice of antibiotic will depend on the sensitivities of the specific strain.¹
• Counselling:
  The case should be advised of the nature of the infection and its mode of transmission.
  Educate about hygiene. Thorough handwashing with soap and water is the single most important control measure. The importance of thorough handwashing after using the toilet and before handling any food must be emphasised. Cases should be advised not to prepare food for others or care for patients or children whilst unwell. Information should be provided to cases for distribution to household contacts. Safer sex practices should be observed until 48 hours after diarrhoea has ceased.
  Advise patients identified as MSM to seek a full sexual health check with their local GP or consult a sexual health clinic.
• Testing:
  Stool specimens must be processed rapidly after collection as Shigella remains viable only for a short period outside the human body.

Contacts

• Contact Tracing:
  Contact tracing should occur in outbreak settings, or in the case of S. dysenteriae infection. Outside of specific outbreak settings, routine contact tracing of infections caused by other serogroups is unnecessary. Where symptomatic contacts are identified incidentally during case follow up, proceed with restriction, investigation and counselling as below.
• Definition:Household members, sexual partners or those exposed to a common source.
• Restriction:
  Symptomatic contacts of a S. dysenteriae case should be treated as a potential case and excluded from food handling, and caring for children, patients or the elderly. On investigation if the faecal culture or PCR is positive the contact should be treated as per confirmed cases above. If the faecal culture or PCR are negative the contact should be excluded until 48hrs after cessation of diarrhoea. Symptomatic contacts of other Shigella species infections identified during case investigation should be excluded whilst unwell and for 48hrs after cessation of diarrhoea, and advised to seek medical advice.
• Counselling:
  Where contact tracing occurs, advise of the nature of the infection and its mode of transmission.
  Educate about hygiene. In particular, thorough handwashing with soap after using the toilet and before handling any food

Summary

For a community outbreak, prepare a report of the investigation for OzFoodNet, Communicable Diseases Branch, Queensland Health, on request.

References

1. Heymann D. (Ed). Control of Communicable Diseases Manual. 20th edition. Washington: American Public Health Association. 2015. 729p.
2. PHLS Advisory Committee on Gastrointestinal Infections. Preventing person-to-person spread following gastrointestinal infections: guidelines for public health physicians and environmental health officers. Commun Dis Public Health. 2004;7(4): 362-3
3. Das JK, Ali A, Salam RA, Bhutta ZA. Antibiotics for the treatment of Cholera, Shigella and Cryptosporidium in children. BMC Public Health, 2013;13(suppl 3):S10. Available from: https://doi.org/10.1186/1471-2458-13-S3-S10
4. Tai AYC, Easton M, Encena J, Rotty J, Valcanis M, Howden BP, Slota-Kan S, Gregory J. A review of the public health management of shigellosis in Australia in the era of culture-independent diagnostic testing. Aust N Z J Public Health. 2016; 20(6)588-91
5. Turabelidze G, Bowen A, Lin M, Tucker A, Butler C, Fick F. Convalescent cultures for control of shigellosis outbreaks. Pediatr infect Dis J. 2010;29(8):728-30

6. Dutta S, Chatterjee A, Dutta P, Rejendran K, Roy S, Pramanik KC, Bhattacharya SK. Sensitivity and performance characteristics of a direct PCR with stool samples in comparison to conventional techniques for diagnosis of Shigella and enterovasive Escherichia coli infection in children with acute diarrhoea in Calcutta, India. National J Med Microbiol. 2001. 50;667-674.
7. Gaudio PA, Sethabutr O, Echeverria P, Hoge CW. Utility of a Polymerase Chain Reaction Diagnostic System in a Study of the Epidemiology of Shigellosis among Dysentery Patients, Family Contacts, and Well Controls Living in a Shigellosis-Endemic Area. J Infect Dis. 1997. 176;1013-1018.
8. Islam MS, Hossain MS, Hasan MK, Rahman MM, Fuchs G, Mahakanabis D, Baqui AH, Albert MJ. Detection of Shigellae from Stools of Dysentery Patients by Culture and Polymerase Chain Reaction Techniques. J Diarrhoeal Dis Res. 1998. 16(4):248-251

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