Shigellosis

Shigellosis caused by the Shigella bacteria is not common in Aotearoa New Zealand and is often acquired overseas. However, locally acquired cases and outbreaks do sometimes occur caused by person-to-person transmission.

There are four species or serogroups of Shigella.

• Group A (S. dysenteriae) associated with more serious disease and complications.
• Group B (S. flexneri).
• Group C (S. boydii).
• Group D (S. sonnei).

Drug-resistant Shigella

Extensively drug-resistant (XDR) and multidrug resistant (MDR) Shigella have emerged in Aotearoa New Zealand in recent years. XDR Shigella strains are resistant to all commonly recommended empiric and alternative antibiotics including ampicillin, ceftriaxone, azithromycin, cotrimoxazole and ciprofloxacin, resulting in significantly limited treatment options for infected individuals with severe illness [1,2]. MDR Shigella strains are resistant to any three of ceftriaxone, azithromycin, cotrimoxazole and ciprofloxacin [3].

From late 2023, XDR Shigella sonnei was associated with an outbreak, with ongoing local transmission, primarily among gay, bisexual, and other men who have sex with men (MSM). The outbreak was genomically linked to an ongoing international cluster, predominantly affecting MSM with cases in Europe, the United Kingdom, and United States.

Of note, detections of MDR and XDR shigellosis cases outside of this cluster are ongoing, including cases of both Shilgella sonnei and S. flexneri.

More detailed epidemiological information is available on the Institute of Environmental Science and Research (ESR) surveillance website.

Information on foodborne illness is available on the Ministry for Primary Industries website.

Further information on enteric diseases is also available Appendix 2: Enteric disease – Health New Zealand | Te Whatu Ora

Acute diarrhoea with fever, abdominal cramps, blood or mucus in stools.

Laboratory definitive evidence for a confirmed case requires isolation of any Shigella species from a stool sample or rectal swab and confirmation of genus by a reference laboratory.

While a polymerase chain reaction (PCR) test may be used for screening, a positive PCR test does not meet the criteria for laboratory confirmation. The PCR target for Shigella detects the ipaH gene which is found in both Shigella and enteroinvasive Escherichia coli. Therefore, positive specimens require culture for confirmation as Shigella.

All isolates must be referred to the Enteric Reference Laboratory at ESR for further characterisation.

• Confirmed: A clinically compatible illness accompanied by laboratory definitive evidence.
• Probable: A clinically compatible illness that is either epidemiologically linked to a confirmed case or has had contact with the same common source as a confirmed case that is part of a common-source outbreak.
• Under investigation: A case that has been notified, but information is not yet available to classify it as probable or confirmed.
• Not a case: A case that has been investigated and subsequently found not to meet the case definition.

Humans.

Range of 12 hours to 1 week; usually 1–3 days.

Direct or indirect faecal-oral transmission. Food or water may become contaminated. Shigella is highly infectious. An infective dose can be as low as 10–100 organisms.

Faecal-oral transmission may also occur through any type of sexual activity that involves contact with faeces (even if faeces is not visible). This includes direct sexual contact (e.g. anal sex, fisting, fingering, rimming, oral sex) or indirect sexual contact (handling contaminated objects such as a condom or sex toy).

Up to 4 weeks after infection. Asymptomatic carriage may also occur. In rare instances, faecal shedding can persist for months. Appropriate antimicrobial treatment (when indicated) reduces the duration of carriage to a few days.

Attending medical practitioners or laboratories must immediately notify the local medical officer of health of suspected cases. Notification should not await confirmation.

Public health services should inform the Protection Clinical team of any new extensively drug-resistant (XDR) Shigella cases for awareness by email to protection.clinical@tewhatuora.govt.nz. No individual identifiable information should be included. 

See Appendix 5: Escalation pathways for more information.

If a culture is positive, ensure a thorough case investigation is conducted if not already completed. Obtain a history of travel, a food history and history of water exposure, as well as a list of possible contacts.

Confirmed cases of shigellosis in males aged 16 or over should be asked if they had any sexual contact with another male/other males during the incubation period. If sexual contact is reported, to assist with outbreak control, any history of visiting sex on site venues, or attending other events where people meet for sex during the incubation period should also be checked and reported in the case report form, including information on names, dates and events.

Sexual transmission of shigellosis may occur through sexual activity involving contact with faeces, including indirect contact through objects (e.g. condoms, sex toys). This should be investigated where applicable, but sexual transmission should not be assumed in every case of shigellosis, including MDR or XDR shigellosis cases

Suggested phrasing for case interviews are provided below (for men aged 16 or over only).

One of the ways Shigella can be passed between people is during sexual activity with someone who has shigellosis. To help us understand how you may have become unwell, and whether it may spread to anyone else, it is important to ask you some questions about recent sexual activity.

When we talk about sex, we mean all types of sexual contact. This includes oral, vaginal, anal sex or other sexual contact.

1. Did you have any sexual contact with another male in the 7 days before you became sick? If yes:
   1. To assist with outbreak control, did you visit any sex on site venues, or attend any events where you met people for sex, in the week before you became sick?
   2. What are the names of these venues or events? And what dates did you visit?

In a healthcare facility, only standard precautions are indicated in most cases. If the case is diapered or incontinent, use contact precautions for the duration of illness. For further details refer to the exclusion and clearance criteria in Appendix 2: Enteric disease.

Where sexual transmission is suspected (e.g. confirmed case with sexual partners during the case’s infectious period and not linked to food or water common source outbreak), the case should be advised not to have any form of sexual contact until 2 weeks after diarrhoea has resolved.

High-risk Shigella boydii, S. dysenteriae, and S. flexneri cases  

Exclusion (see Appendix 2: Enteric disease) is required until two consecutive negative faecal specimens are obtained, taken at least 48 hours apart, and at least 48 hours after completing any antibiotic course.

XDR Shigella cases

Exclusion and clearance requirements for XDR Shigella cases are the same as for fully sensitive cases (see appendix 2: enteric disease).

Advise the shigellosis case and their caregivers of the nature of the infection and its mode of transmission. Educate about hand and food hygiene.

For both men and women, abstinence from sexual activity until 2 weeks after diarrhoea has resolved is recommended—this particularly applies to oral-anal contact.

Additional follow up and advice for all shigellosis cases where sexual transmission is suspected.

• Ensure efforts are made to trace all sexual contacts of the case to advise them of their exposure, educate about shigellosis, and to seek medical advice if symptomatic. This could be done by providing the case with the Shigellosis in MSM information sheet and Burnett Foundation resources and encouraging them to share these with their sexual contacts, or through standard contact tracing processes.
• Advise the case not to have any form of sexual contact until 2 weeks after diarrhoea has resolved.
• People with sexually acquired shigellosis may have other sexual health needs that would benefit from review at a sexual health service. Encourage the case to attend their local sexual health service or GP for a sexual health screen (if not recently done).

Additional follow up for multi or extensively drug-resistant shigellosis cases.

• Follow up with the case 3 weeks after symptom onset to confirm resolution of symptoms. If symptoms persist, recommend that case consults with their GP for consideration of further testing or management. 

A contact is anyone who had:

• close contact (e.g. household) with a case during their illness or the subsequent period of communicability
• been exposed to the same contaminated food or water in a common-source outbreak
• sexual contact with a case during their illness or subsequent period of communicability. 

All close (for example, household) contacts in one of the high-risk groups (1–4, see the exclusion and clearance criteria in Appendix 2: Enteric disease) should be asked to provide clearance of one negative faecal sample. Contacts with symptoms, even mild, should be investigated as cases.

For high-risk groups and symptomatic contacts (enteric or otherwise) refer to the exclusion and clearance criteria in Appendix 2: Enteric disease.

Shigella boydii, S. dysenteriae and S. flexneri

All close (e.g. household) contacts in one of the high-risk groups (see the exclusion and clearance criteria in Appendix 2: Enteric disease) should be excluded until one negative faecal sample has been provided. Contacts with symptoms, even mild, should be investigated as cases.

Shigella sonnei

No clearance samples are required for contacts.

Multi or extensively drug-resistant Shigella species

The same exclusion and clearance requirements as fully sensitive Shigella species.

Nil.

Advise all contacts of the incubation period and typical symptoms of shigellosis, importance of hand hygiene and to seek early medical attention if symptoms develop.

If sexual transmission is suspected.

• Ensure efforts are made to trace all contacts of cases to advise them of their exposure, educate about shigellosis, and to seek medical advice if symptomatic. This can be done by providing the contact with the Shigellosis in MSM information sheet and Burnett Foundation resources (for MSM), or by encouraging the case to share these with their sexual contacts.

Check for other cases in the community. Investigate potential food or water sources of infection if there is a cluster of cases or an apparent epidemiological link.

If indicated, check the water supply for microbiological contamination and compliance with the latest New Zealand drinking-water standards [4].

Where sexual transmission is suspected, investigation should establish if any sex on site premises are reported to assist with outbreak control.

Clean and disinfect surfaces and articles soiled with stools. For further details, refer to Appendix 1: Disinfection.

In an outbreak, consider a media release and/or direct communication with local parents, early childhood services, schools and health professionals to encourage prompt reporting of symptoms and appropriate testing. In communications with doctors, include recommendations regarding diagnosis, treatment and infection control.

In early childhood services or other institutional situations, ensure satisfactory facilities and infection control practices regarding:

• hand cleaning
• nappy changing
• toilet use and toilet training
• preparation and handling of food
• cleaning of sleeping areas, toys and other surfaces.

Educate the public about safe food preparation (see Appendix 3: Patient information).

All gay, bisexual, and other men who have sex with men (MSM) with possible sexually acquired shigellosis, and their sexual contacts should be provided with the following resources: Shigella Infection Among Gay, Bisexual, and Other Men who Have Sex With Men (cdc.gov) and Shigella (burnettfoundation.org.nz)

Where sex on site premises have been identified, guidance to these premises, and to sex workers includes encouraging minimising faecal-oral exposures during sexual activity by use of barriers during sex, washing genitals and anal area before and after sex, and washing sex toys after use.

Ensure complete case information is entered into EpiSurv.

Where food/food businesses are thought to be involved inform the Ministry for Primary Industries.

If a cluster of cases occurs, public health services should inform the Protection Clinical Team for awareness by email to protection.clinical@tewhatuora.govt.nz, to inform outbreak liaison staff at ESR, and complete the Outbreak Report Form.

1. Centers for Disease Control and Prevention. (n.d.). Health Alert Network (HAN) - 00486 | Increase in extensively drug-resistant Shigellosis in the United States. Retrieved from https://wwwnc.cdc.gov/eid/article/22/6/15-2088_article
2. Ingle, D. J., Easton, M., Valcanis, M., Seemann, T., Kwong, J. C., Stephens, N., ... & Howden, B. P. (2016). Emergence of extensively drug-resistant and multidrug-resistant Shigella flexneri serotype 2a associated with sexual transmission among gay, bisexual, and other men who have sex with men, in England: A descriptive epidemiological study. The Lancet Infectious Diseases, 16(6), 659-668. https://doi.org/10.1016/S1473-3099(16)30004-X
3. Baker, K. S., Dallman, T. J., Ashton, P. M., Day, M., Hughes, G., Crook, P. D., ... & Jenkins, C. (2022). Intercontinental dissemination of extensively drug-resistant and multidrug-resistant Shigella sonnei: A descriptive epidemiological study. The Lancet Infectious Diseases, 23(1), 56-65. https://doi.org/10.1016/S1473-3099(22)00807-6
4. New Zealand Government. (2022). Water Services (Drinking Water Standards for New Zealand) Regulations 2022 (LI 2022/168). New Zealand Legislation. Retrieved from https://www.legislation.govt.nz/regulation/public/2022/0168/latest/whole.html