L4 Public Health Control of infectious diseases

Overview

This lecture covers the control of infectious disease from a public health perspective: its historical development in Aotearoa, and the modern framework of controls used today — improved sanitation/baseline health/health care/clean water & food/living conditions, antimicrobials, vaccination, surveillance, legislation & regulations (international and national), and preparedness. It also covers the principles underpinning immunisation as a population-based health strategy.

Historical control of infectious disease in Aotearoa

• John Snow and cholera (1854 London): drew a ‘dot map’ of cholera case clusters, discounted the prevailing ‘miasma’ theory, and traced cases to the contaminated Broad Street water pump (>600 deaths); closed down the pump.
• Māori customary practices served as infectious disease controls: tapu kept the sick, the dead, and their possessions separate; hygiene and sanitation used separate toileting and food compost areas; leftovers were not consumed; human bodily products were disposed of; a separate whare was used for the birth period.
• Colonisation: explorers and colonists brought new diseases (TB, influenza, typhoid, measles, smallpox, STIs) to a Māori population with no immunity. Many deaths occurred on migrant ships, especially among infants, from GI infections and scarlet fever. Smallpox vaccination began in the 1840s; quarantine regulations from 1870 (e.g. Ōtamahua/Quail Island).
• Declining morbidity and mortality from infectious disease over time: about one-third of deaths in the 1870s were from infectious disease; down to 15% by 1900 (with the 1918 influenza pandemic noted alongside this period); under 7% by 2000; under 4.5% by 2021 (2022 deaths rose exponentially again due to the COVID-19 pandemic).

Sanitation, antimicrobials and TB

• TB has shown declining rates in high-income countries since WWII, driven by improved baseline health/health care/living conditions, antimicrobial treatment and screening, surveillance, and vaccination.
• In Aotearoa, TB rates showed a relative plateau from the 1980s due to incoming cases, with a slight decline since 2015.
• TB remains the world’s leading single infectious disease killer in 2024 (it was briefly overtaken by COVID-19).

Water safety: chlorination and the Havelock North outbreak

• Water Services Act 2021 requires water suppliers to provide ‘residual disinfection’ in pipe networks; chlorine is most commonly used as it is safe, effective and affordable.
• Havelock North 2016: routine testing on 11.08.2016 showed E. coli, triggering a boil water notice and chlorination; on 12.08.2016 the Medical Officer of Health was alerted to a rise in diarrhoeal disease presenting to Hawke’s Bay Hospital.
• Up to 8320 cases (of 14,118 residents) of campylobacteriosis were linked to a contaminated water supply (sheep faeces): 4 deaths, 3 cases of Guillain-Barré syndrome, 42 hospitalisations.

Vaccination as a population-based strategy

Key strategies: the immunisation schedule (recorded on the Aotearoa Immunisation Register); funded vaccines (e.g. free flu shots for pregnant people, those >65, and those with co-morbidities); catch-up campaigns and promotion; place-based vaccination (e.g. HPV delivered at schools); mandates/requirements; and outbreak-specific approaches (ring vaccination, post-exposure vaccination, mass vaccination, mobile/fixed-site/door-to-door delivery, mandates).

National Immunisation Schedule (from 1 July 2024), by stage:

• Pregnancy: tetanus+diphtheria+pertussis (Boostrix®); influenza.

• 6 weeks: rotavirus (Rotarix® oral, 1st dose before 15 weeks); diphtheria+tetanus+pertussis+polio+hepatitis B+Hib (Infanrix® hexa); pneumococcal (Prevenar 13®).

• 3 months: rotavirus (Rotarix®, 2nd dose before 25 weeks); Infanrix® hexa; meningococcal B (Bexsero®, can start at 8 weeks).

• 5 months: Infanrix® hexa; Prevenar 13®; Bexsero® (can be given at 4 months).

• 12 months: MMR (Priorix®); Prevenar 13®; Bexsero®.

• 15 months: Hib (Act-HIB®); MMR (Priorix®); varicella (Varilrix®).

• 4 years: diphtheria+tetanus+pertussis+polio (Infanrix® IPV).

• 9-13 years: HPV (Gardasil®9, 2 doses 6 months apart); Tdap (Boostrix®, from 11 years).

• 45 years: Tdap (Boostrix®).

• 65 years: Tdap (Boostrix®); influenza; shingles (Shingrix®, 2 doses 2-6 months apart).

• Immunisation Advisory Centre: advises the health workforce via the Immunisation Handbook (clinical guidelines based on up-to-date evidence), and conducts research, e.g. the Te Hunga Manenei study of whānau views on access to immunisation, aiming to understand why some tamariki are not vaccinated on time.

• Of the 5 NZ Health Targets 2024, one is improved immunisation: 95% of children fully immunised at 24 months of age by 2030.

• Measles: over 100,000 deaths globally in 2023, most among un/under-vaccinated children under 5; MMR is given at 12 and 15 months on the schedule.

Basic reproduction number and herd immunity

• Basic reproduction number (R0): the number of cases expected to be generated by one case in a susceptible population, determined by infectivity (probability of infection given contact), duration of infectiousness, and pattern of mixing (rate of contact per time).
• R0 < 1: disease will not spread. R0 = 1: disease becomes endemic. R0 > 1: epidemic or pandemic.
• Example R0 values: Delta ~5; measles 12-18.
• Herd immunity threshold (HIT) derivation: if proportion p of the population is immunised, p×R0 escape infection (e.g. 0.8×18 = 14.4). To find the threshold that prevents an epidemic: R0×S = 1, where S is the susceptible population; S can be rewritten as (1 − p); so R0×(1 − p) = 1, giving (1 − p) = 1/R0, so the herd immunity threshold is $p\ge 1-1/R0$.
• Worked examples: for Delta (R0 ~5), 1 − 1/5 = ~80% must be vaccinated; for measles (R0 ~18), 1 − 1/18 = ≥94% must be vaccinated.
• Across diseases, HIT rises with R0: influenza (R0=1, HIT=0%), SARS (R0=1.6-2, HIT37.5-50%), COVID-19 ancestral (R02.5-4, HIT60-75%), COVID-19 Alpha (R04-5, HIT75-80%), COVID-19 Delta (R05-8, HIT80-87.5%), chickenpox (R010-12.5, HIT90-92%), measles (R012-18, HIT~92-95%).

MMR coverage inequities

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MMR1 and MMR2 coverage rates for birth cohorts 2017-2020, by ethnicity: MMR1 coverage is generally at or above the 90% reference line for all groups except Māori, which dips below 90% (as low as ~80% for the 2020 cohort). MMR2 coverage is markedly lower than MMR1 across all groups (roughly 50-90%), with Māori again among the lowest (as low as ~50% for the 2018 cohort) and Asian showing the highest MMR2 coverage (up to ~90%).

Surveillance

Surveillance is the ongoing and systematic collection of routine data, which is analysed, interpreted and acted upon to identify outbreaks and new pathogens, and to monitor trends and describe the current burden of disease.

• Passive surveillance: notifiable diseases, sentinel site surveillance, analysis of routinely collected data, environmental surveillance.
• Active surveillance: contact tracing, outbreak investigation, environmental, zoonotic.

Global Influenza Surveillance and Response System (GISRS): the first influenza vaccine was developed in 1942; WHO GISRS was established in 1952 and now has 127 participating countries; WHO advises biannually on vaccine composition for the Northern and Southern Hemispheres; it acts as a global alert mechanism for the emergence of respiratory viruses with pandemic potential, and is expanding to include other priority respiratory viruses such as RSV and COVID-19.

Influenza evolution mechanisms underlying this surveillance need:

• Antigenic drift: accumulation of small mutations on the virus surface proteins over time, causing minor antigenic change with epidemic potential.
• Antigenic shift: major antigenic change with pandemic potential, arising either by a direct jump (an avian virus adapts directly and jumps to humans) or by genetic reassortment (avian and human viral genes reassort within a swine host, producing a new virus that then jumps to humans).

ILI (influenza-like illness) surveillance in Aotearoa: ESR has been part of WHO GISRS since 1989, on behalf of the NZ Ministry of Health. Each week at sentinel sites, GPs and nurses swab patients with ILI; swabs go to ESR’s National Influenza Centre and are tested for influenza, SARS-CoV-2, RSV, adenovirus, enterovirus, metapneumovirus, parainfluenza and rhinovirus. Data is sent to WHO GISRS and published on the EpiSurv database, the ESR respiratory illness dashboard, and in reports.

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Other ESR dashboards cover: invasive pneumococcal disease, meningococcal disease, measles, pertussis, STIs (syphilis, chlamydia, gonorrhoea), wastewater (COVID-19), and notifiable diseases.

Notifiable diseases are outlined in Schedules 1 and 2 of the Health Act 1956, and are notifiable to the Medical Officer of Health, who undertakes investigation, contact tracing, control measures and communication. Diseases notifiable in New Zealand (as of Feb 2025):

• Section A (notifiable to Medical Officer of Health and Local Authority): acute gastroenteritis, campylobacteriosis, cholera, cryptosporidiosis, giardiasis, hepatitis A, legionellosis, listeriosis, primary amoebic meningoencephalitis, salmonellosis, shigellosis, typhoid and paratyphoid fever, yersiniosis.
• Section B (notifiable to Medical Officer of Health): anthrax, arboviral diseases, brucellosis, COVID-19, Creutzfeldt-Jakob disease (CJD) and other spongiform encephalopathies, Cronobacter species, diphtheria, Haemophilus influenzae b, hepatitis B, hepatitis C, hepatitis (viral) not otherwise specified, hydatid disease, Highly Pathogenic Avian Influenza (incl. H5N1), invasive group A streptococcal infection, invasive pneumococcal disease, leprosy, leptospirosis, malaria, measles, Middle East Respiratory Syndrome (MERS), monkeypox (mpox), mumps, Neisseria meningitidis invasive disease, non-seasonal influenza (transmissible between humans), novel coronavirus capable of causing severe respiratory illness, pertussis, plague, poliomyelitis, Q fever, rabies and other lyssaviruses, rheumatic fever, rickettsial diseases, rubella, SARS, tetanus, tuberculosis (all forms), verotoxin/Shiga toxin-producing E. coli, viral haemorrhagic fevers, yellow fever.
• Section C (notifiable without identifying information of the patient/deceased): AIDS, gonorrhoeal infection, HIV infection, syphilis.
• Also notifiable to the Medical Officer of Health (not “notifiable infectious diseases”): cysticercosis, decompression sickness, lead absorption ≥0.24 µmol/l (5µg/dl), poisoning from chemical contamination of the environment, taeniasis, trichinosis.

Notifiable disease surveillance system flow: people with illness consult clinicians → clinicians take samples to laboratories → laboratories notify clinicians and local Medical Officers of Health (via electronic notification data on EpiSurv) → local disease control measures. Local Medical Officers of Health also feed into ESR → National Public Health Service/Public Health Agency → national disease control measures. Epidemiological information (regular and ad hoc reports, the surveillance website) links to ESR.

AIDS/HIV notification: the Health Act 1956 covers notification of AIDS, HIV, gonorrhoea and syphilis without identifying information; HIV became notifiable in 2017 (Health (Protection) Amendment Act). The laboratory enters data onto EpiSurv and the Medical Officer of Health is notified; the AIDS Epidemiology Group (AEG) sends the ordering health provider a webform link for more detailed information, and the AEG reports via the Ministry of Health and Medical Officers of Health, an annual AIDS-NZ newsletter, and an AEG dashboard.

Novel pathogen surveillance — WHO early COVID-19 response timeline: 31.12.2019 WHO China Country Office informed of a cluster of pneumonia of unknown etiology in Wuhan; 01.01.2020 WHO Incident Management Support Team set up; 05.01.2020 WHO Disease Outbreak News on “pneumonia of unknown cause”, with a global surveillance system implemented across WHO regional offices and technical advice provided; 10.01.2020 genetic sequence shared by China, enabling test development; 11.01.2020 first death in China; 13.01.2020 first case outside China; 20/21.01.2020 WHO field trip to Wuhan; 22.01.2020 WHO mission reported human-to-human transmission; 22/23.01.2020 Emergency Committee met under the 2005 IHR to assess a possible PHEIC — no consensus; 30.01.2020 Emergency Committee met again and declared a PHEIC; 28.02.2020 first case in NZ; 09.03.2020 COVID-19 made notifiable under an NZ Health Act 1956 amendment; 11.03.2020 WHO declared a pandemic.

Legislation and regulation: international

The 2005 International Health Regulations (IHR) are a legal requirement for Member States and signatories to detect public health risks and emergencies via surveillance systems; assess and report to WHO events that may constitute a PHEIC, within 48 or 24 hours (e.g. SARS and wildtype polio must be reported within 24h); and respond to public health risks and emergencies. The earliest such agreement was in 1851, with the first WHO International Sanitary Agreement in 1951. WHO’s role is to conduct global surveillance and assessment, support Member States with technical assistance, and determine PHEICs.

A Public Health Emergency of International Concern (PHEIC) is defined as “an extraordinary event which is determined to constitute a public health risk to other States through the international spread of disease and to potentially require a coordinated international response.” Under the 2005 IHR, all 194 Member States have a legal duty to respond to a PHEIC. There have been 8 PHEIC declarations so far: swine flu, polio, Ebola (x2), Zika, COVID-19, mpox (x2).

2024 update to the IHR: introduced a “pandemic emergency” definition representing a higher level of alarm — “a communicable disease that has, or is at high risk of having, wide geographical spread to and within multiple States, exceeds or is at high risk of exceeding the capacity of health systems to respond in those States; causes, or is at high risk of causing, substantial social and/or economic disruption, including disruption to international traffic and trade; and requires rapid, equitable and enhanced coordinated international action, with whole-of-government and whole-of-society approaches.” The update also affirmed a commitment to solidarity and equity, and created National IHR Authorities.

Legislation and regulation: New Zealand

There were multiple and various Acts pertaining to health through the 19th and early 20th centuries, followed by the 1920 Health Act, then the 1956 Health Act (still in force, with many amendments). The 2020 COVID-19 Public Health Response Act (now repealed) enabled border closures, vaccine mandates, Alert Levels, isolation and quarantine requirements, and masks. The 2022 Pae Ora (Healthy Futures) Act established the Public Health Agency, Te Whatu Ora/Health NZ, and the Māori Health Authority (since disestablished).

Special powers of the Medical Officer of Health (Part 3, section 70 of the Health Act 1956): for the purpose of preventing outbreak or spread of infectious disease, Medical Officers of Health, if authorised by the Minister of Health or if a state of emergency has been declared, may require isolation, testing, quarantine, closure, disinfection, forbidding congregations, and inspections. Medical Officers of Health can also issue public health orders or directions to manage infectious disease in non-emergency settings, e.g. requiring compliance with contact tracing, treatment and isolation for TB.

Six overarching principles for using infectious disease management measures: 1) respect for individuals — take into account special circumstances; 2) voluntary compliance — give individuals the option to comply before issuing an order/directive; 3) individual to be informed about the disease management measures; 4) principle of proportionality — proportionate to the public health risk; 5) least restrictive alternative — apply the least restrictive measure that will achieve the objective of minimising public health risk; 6) measures apply no longer than necessary — though this can be quite long, e.g. 6 months for TB.

Preparedness and outbreak management

Definitions:

• Outbreak: “an epidemic limited to a localised increase in the incidence of a disease, e.g., in a village, town, or closed institution.”
• Epidemic: “the occurrence in a community or region of cases of an illness, specific health-related behaviour, or other health-related events clearly in excess of normal expectancy.”
• Pandemic: “an epidemic occurring worldwide, or over a very wide area, crossing international boundaries and usually affecting a large number of people.”

Preparation is the first step in outbreak management. Components of outbreak management, under the overarching aim of minimising the public health impact of disease outbreaks:

• Preparation: achieve an optimal level of preparedness.
• Surveillance: consistent and comprehensive collection and review of information on diseases with outbreak potential.
• Confirmation and assessment: sensitive, specific and timely detection of potential outbreaks with public health impact.
• Outbreak description (situational analysis and descriptive epidemiology): characterise the outbreak to identify the immediate need for control or hypotheses for further investigation.
• Full investigation (analytic epidemiological, environmental, and laboratory investigation): identify the outbreak source, transmission mechanisms, contributing factors and control points.
• Outbreak control: prevent further disease transmission.
• Outbreak communication: keep the public and relevant agencies appropriately informed and involved.
• Outbreak documentation: optimal dissemination of recommendations.

Outbreak management framework flow: Preparation → Surveillance → Outbreak investigation (Confirmation and assessment → Outbreak description → Full investigation [analytic epidemiology, environmental, laboratory components]), which connects bidirectionally with Outbreak response (Outbreak control ↔ Outbreak communication ↔ Outbreak documentation); Outbreak documentation also loops back up to Preparation.

Pandemic planning uses 3 broad strategies:

1. Mitigation — manageable for the health system, “flatten the curve”.
2. Suppression — keep transmission low to minimise adverse health effects (e.g. HIV/AIDS).
3. Elimination — zero community transmission.

The 2017 ‘NZ Influenza Pandemic Plan’ was intended for all respiratory viruses, and assumed influenza could not be eliminated. In practice, NZ’s COVID-19 response pursued elimination from March 2020 to late 2021 (strict border controls, lockdowns, isolation, quarantine, social distancing, testing and contact tracing, risk communication, masks, vaccination including mandates), then shifted to mitigation from February 2022 (continued vaccination, surveillance of cases and wastewater, improving air quality, self-RAT testing/isolation, masks). A 2024 ‘NZ Pandemic Plan’ has since been produced.

Self-test

1. Describe how John Snow identified the source of the 1854 London cholera outbreak, and what theory this disproved.
2. List the customary Māori practices described as controls of infectious disease.
3. Describe the trend in the proportion of NZ deaths due to infectious disease from the 1870s to 2022, and name the two pandemics noted alongside this decline.
4. Explain why TB rates declined in high-income countries since WWII, and why Aotearoa’s TB rate plateaued from the 1980s.
5. Describe what happened in the Havelock North 2016 outbreak, including its cause and health impact.
6. Define the basic reproduction number (R0) and list the three factors that determine it.
7. Derive the herd immunity threshold formula from R0, and calculate the threshold for measles (R0 ~18).
8. What does the MMR1 vs MMR2 coverage data by ethnicity show about vaccination equity in Aotearoa?
9. Distinguish passive surveillance from active surveillance, giving examples of each.
10. Distinguish antigenic drift from antigenic shift, including how antigenic shift can arise.
11. Describe the role and structure of the Global Influenza Surveillance and Response System (GISRS).
12. Describe the pathway a notifiable disease case follows from patient to national disease control measures.
13. Explain how HIV/AIDS notification differs from most other notifiable diseases in Aotearoa.
14. Outline the key events in the WHO’s early response to COVID-19, from the first report to the declaration of a pandemic.
15. Define a Public Health Emergency of International Concern (PHEIC) and state how many have been declared.
16. What three obligations does the 2005 International Health Regulations place on Member States?
17. Describe the special powers available to a Medical Officer of Health under Part 3 section 70 of the Health Act 1956.
18. List the six overarching principles that must be applied when using infectious disease management measures.
19. Distinguish mitigation, suppression and elimination as pandemic strategies, and state which NZ used and when during COVID-19.
20. A rural water supply tests positive for E. coli and cases of gastroenteritis begin rising in the surrounding community. Using the outbreak management framework, describe the sequence of steps that should follow from this point, and identify which control measures (sanitation/vaccination/legislation/surveillance) are relevant.

Answers

Reveal answers

1. Snow plotted a ‘dot map’ of cholera case clusters in 1854 London, showing they clustered around the Broad Street water pump; this traced the source to contaminated water and disproved the prevailing ‘miasma’ (bad air) theory. There were over 600 deaths, and the pump was closed down.
2. Tapu kept the sick, dead and their possessions separate; separate toileting and food compost areas were used; leftovers were not consumed; human bodily products were disposed of; a separate whare was used for the birth period.
3. About one-third of deaths in the 1870s were from infectious disease, falling to 15% by 1900, under 7% by 2000, and under 4.5% by 2021. The 1918 influenza pandemic is noted alongside the 1900 figure, and 2022 deaths rose exponentially again due to the COVID-19 pandemic.
4. TB declined due to improved baseline health, health care and living conditions, antimicrobial treatment and screening, surveillance, and vaccination. In Aotearoa the rate plateaued from the 1980s due to incoming cases (with a slight decline since 2015).
5. Routine testing on 11.08.2016 detected E. coli, prompting a boil water notice and chlorination; a rise in diarrhoeal disease was noticed at Hawke’s Bay Hospital the next day. Up to 8320 of 14,118 residents developed campylobacteriosis from a water supply contaminated with sheep faeces, causing 4 deaths, 3 cases of Guillain-Barré syndrome, and 42 hospitalisations.
6. R0 is the number of cases expected to be generated by one case in a susceptible population. It is determined by infectivity (probability of infection given contact), duration of infectiousness, and pattern of mixing (rate of contact per time).
7. Setting R0×S = 1 (where S is the susceptible proportion) and substituting S = (1 − p) gives R0×(1 − p) = 1, so (1 − p) = 1/R0, and the herd immunity threshold is p ≥ 1 − 1/R0. For measles, 1 − 1/18 = ≥94% must be vaccinated.
8. MMR1 coverage is near or above the 90% target for most ethnicities but dips below 90% for Māori (as low as ~80%). MMR2 coverage is markedly lower for all groups (~50-90%), with Māori again among the lowest (~50%) and Asian the highest (~90%), showing a persistent equity gap, especially for the second dose.
9. Passive surveillance relies on routinely reported/collected data: notifiable diseases, sentinel site surveillance, analysis of routine data, environmental data. Active surveillance involves deliberately seeking cases: contact tracing, outbreak investigation, environmental investigation, zoonotic surveillance.
10. Antigenic drift is the gradual accumulation of small mutations on virus surface proteins, causing minor antigenic change with epidemic potential. Antigenic shift is a major antigenic change with pandemic potential, arising either from a direct jump of an avian virus adapting to humans, or from genetic reassortment of avian and human viral genes within a shared host such as a pig.
11. GISRS was established by WHO in 1952 (the first flu vaccine was developed in 1942) and now has 127 participating countries. It advises biannually on vaccine composition for the Northern and Southern Hemispheres, acts as a global alert mechanism for pandemic-potential respiratory viruses, and is expanding to include RSV and COVID-19.
12. A person with illness consults a clinician, who takes samples sent to a laboratory; the laboratory notifies clinicians and the local Medical Officer of Health (via EpiSurv), triggering local disease control measures. Local Medical Officers of Health also feed data to ESR, which feeds the National Public Health Service/Public Health Agency, informing national disease control measures.
13. HIV/AIDS notification (along with gonorrhoea and syphilis) must not include identifying information about the patient, unlike most other notifiable diseases. HIV became notifiable only in 2017. The AIDS Epidemiology Group sends the ordering health provider a webform for more detail and reports via the Ministry of Health, an annual newsletter, and its own dashboard.
14. WHO was informed of a pneumonia cluster in Wuhan on 31.12.2019, set up an incident team on 01.01.2020, and issued its first Disease Outbreak News on 05.01.2020. China shared the genetic sequence on 10.01.2020. Human-to-human transmission was confirmed after a WHO field trip (20-22.01.2020). An Emergency Committee found no PHEIC consensus on 22/23.01.2020 but declared one on 30.01.2020. NZ recorded its first case on 28.02.2020 and made COVID-19 notifiable on 09.03.2020; WHO declared a pandemic on 11.03.2020.
15. A PHEIC is “an extraordinary event which is determined to constitute a public health risk to other States through the international spread of disease and to potentially require a coordinated international response.” There have been 8 PHEIC declarations: swine flu, polio, Ebola (x2), Zika, COVID-19, mpox (x2).
16. Member States must: detect public health risks and emergencies via surveillance systems; assess and report to WHO events that may constitute a PHEIC (within 48 or 24 hours depending on the disease); and respond to public health risks and emergencies.
17. If authorised by the Minister of Health or during a declared state of emergency, a Medical Officer of Health may require isolation, testing, quarantine, closure, disinfection, forbidding congregations, and inspections, for the purpose of preventing the outbreak or spread of infectious disease.
18. Respect for individuals; voluntary compliance; the individual to be informed; principle of proportionality; least restrictive alternative; and measures to apply no longer than necessary.
19. Mitigation keeps the outbreak manageable for the health system (“flatten the curve”); suppression keeps transmission low to minimise adverse health effects (e.g. as used for HIV/AIDS); elimination aims for zero community transmission. NZ used elimination from March 2020 to late 2021, then shifted to mitigation from February 2022.
20. Following the outbreak management framework: preparation should already be in place; surveillance detects the rising case numbers; confirmation and assessment establishes this is a genuine outbreak; outbreak description characterises its extent; full investigation (analytic epidemiological, environmental and laboratory) identifies the water supply as the source; outbreak control measures follow (e.g. a boil water notice and chlorination, i.e. sanitation control); outbreak communication informs the public and agencies; and outbreak documentation records recommendations, feeding back into future preparation. Relevant control categories here are primarily sanitation/water control and surveillance, with legislation (e.g. the Water Services Act 2021, Medical Officer of Health powers) underpinning the response.