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Legionnaires’ disease · Symptoms · Who is at risk · Prevention
Key facts
- Cause mostly Legionella pneumophila serogroup 1
- How you catch it breathing in droplets or aspirating water, not by drinking water normally
- Contagious? as a rule no, with one probable exception recorded in Portugal in 2014
- Incubation 2 to 10 days, sometimes up to 14 (CDC) or 16 (WHO)
- South Africa 93 notified cases, January 2018 to September 2020 (NICD)
- Deaths 15 of 74 South African notified cases with a known outcome (20.3 percent)
- Vaccine none, so prevention happens in the water
Prevention happens on the shift, not in the boardroom
The people who flush outlets, clean showerheads and read thermometers decide whether Legionella grows in your building. Legionella Awareness Training gives them the four conditions it needs, the temperature numbers and what to report, in four hours on a phone. R799 a person, HPCSA CPD accredited.
What is Legionnaires’ disease?
Legionnaires’ disease is the severe, pneumonia form of legionellosis, the group of illnesses caused by Legionella bacteria. The milder form is Pontiac fever, a flu-like illness without pneumonia. The disease got its name in Philadelphia in 1976, when an outbreak linked to an American Legion convention caused 182 cases and 29 deaths, spread through the air around the headquarters hotel.
Legionella lives naturally in fresh water in low numbers. The trouble starts when it multiplies in man-made water systems. Most disease is caused by Legionella pneumophila, particularly serogroup 1: in Europe in 2024, 95 percent of culture-confirmed cases were L. pneumophila and over 75 percent of those were serogroup 1 (ECDC).
What are the symptoms of Legionnaires’ disease?
The CDC lists cough, fever, headache, muscle aches and shortness of breath, and says confusion, diarrhoea or nausea can also occur. Those are the symptoms of most pneumonias, so a doctor cannot pick out Legionnaires’ disease by symptoms alone. A chest X-ray confirms pneumonia, and a urine test or a laboratory test on sputum shows whether Legionella is the cause.
Symptoms usually start 2 to 10 days after exposure (NICD, WHO), sometimes up to 14 days (CDC) and up to 16 days in some outbreaks (WHO). That delay is why a hotel guest has usually gone home before falling ill. In South Africa, 87.1 percent of notified cases from 2018 to 2020 were diagnosed with the urinary antigen test, which detects L. pneumophila serogroup 1, so a negative urine test does not rule out other serogroups or species. The CDC says the disease is treated with antibiotics. There is no vaccine.
| Legionnaires’ disease | Pontiac fever | |
|---|---|---|
| What it is | A severe pneumonia | A milder flu-like illness without pneumonia |
| Main symptoms (CDC) | Cough, fever, headache, muscle aches, shortness of breath. Sometimes confusion, diarrhoea or nausea | Fever, muscle aches, headache |
| Time from exposure | 2 to 10 days, sometimes up to 14 (CDC) or 16 (WHO) | A few hours to 48 hours |
| Share of exposed people who fall ill (WHO 2007) | 0.1 to 5 percent in the general population, 0.4 to 14 percent in hospitals | Up to 95 percent |
| How serious | About 1 in 10 die (CDC), about 1 in 4 if caught during a healthcare stay. 98.8 percent of South African notified cases were hospitalised | Illness usually lasts 2 to 5 days (WHO) |
Is Legionella contagious?
As a rule, no. The CDC, the HSE and WHO all say Legionnaires’ disease does not, in general, spread from person to person. The literature records one probable exception, in the 2014 Vila Franca de Xira outbreak in Portugal (New England Journal of Medicine, 2016).
You catch it from water, by breathing in small droplets (aerosol, mist or spray) that contain the bacteria, or by aspiration, when water goes down the wrong way into the lungs (WHO, CDC). Drinking water that goes into the stomach normally is not the route. So when two people from one building fall ill, look at the water they shared, not at each other.
What causes Legionnaires’ disease in South African buildings?
Legionella becomes a risk when four conditions line up: the bacteria are present, the water sits in the growth range (20 to 45 °C, per the HSE), it has food and shelter in stagnant water, biofilm, scale and sludge, and there is a way out to people as droplets small enough to breathe. Break any one and the risk falls. In South African buildings the same failures come up again and again:
- Hot water kept too cool. Geysers turned down or switched off on timers to save electricity, heat pumps set below 60 °C. Stellenbosch University modelling found the lower surfaces of horizontal geysers stay below 45 °C, and the authors concluded that the pipework downstream is where growth is favoured (Stone et al., 2018).
- Roof and JoJo-type tanks added after water outages, which warm up in summer. A 2025 study found L. pneumophila in 14 of 15 residential high-rise buildings sampled in Hillbrow, Johannesburg. All of them used storage tanks, 93 percent of them plastic (Buthane et al., Microorganisms, 2025).
- Closed buildings and empty rooms. The NICD’s authors note that buildings closed for long periods, as in the COVID-19 lockdown, carry a higher risk.
- Cooling towers and evaporative condensers on hotel, office and hospital roofs, and on the ammonia plant of dairies and meat plants.
Most of this is preventable. Of 27 outbreaks the CDC investigated in the USA from 2000 to 2014, 23 (85 percent) had problems a water management programme could have prevented. See our guides to hot water temperature and cooling towers.
Who is most at risk of Legionnaires’ disease?
Most people exposed do not fall ill. The CDC lists the people at higher risk as those aged 50 or over, current or former smokers, and people with chronic lung disease such as COPD or emphysema, a weakened immune system, cancer, diabetes, kidney failure or liver failure. WHO says 75 to 80 percent of cases are over 50 and 60 to 70 percent are male.
South Africa adds its own profile. In NICD sentinel surveillance from 2012 to 2014 at Klerksdorp-Tshepong and Edendale hospitals, Legionella was found in 21 of 1 805 patients (1.2 percent) with severe respiratory illness. Most had HIV, TB or both, and 4 of the 21 (20 percent) died.
Healthcare is where it is deadliest: healthcare settings accounted for 85 percent of deaths in the US outbreaks the CDC investigated from 2000 to 2014. A published South African case from 2017 describes a two-week-old baby whose infection was linked by whole genome sequencing to a hospital water system. The buildings that matter most are frail care centres, hospitals, clinics, retirement villages and hotels with older guests.
Free tool: walk your building and see where the risk sits
The free Legionella Water Walk is a 24-point walkround of hot and cold water, outlets, cooling towers and the other systems that make spray. Every “No” becomes a ranked finding you can export.
Try the free Water Walk, then learn to act on what it finds in Legionella Awareness Training (R799).
How common is Legionnaires’ disease in South Africa?
The official count understates it. This is what the published data shows.
| Measure | Figure | Source |
|---|---|---|
| Notified cases, 1 January 2018 to 30 September 2020 | 93 (43 in 2018, 25 in 2019, 25 in 2020 to September) | NICD Public Health Bulletin, Wolter et al., 2020 |
| Cases from the Western Cape | 72 of 93 (77.4 percent), put down to more awareness and testing there, not more disease | NICD Public Health Bulletin, 2020 |
| Hospitalised | 98.8 percent | NICD Public Health Bulletin, 2020 |
| Died, of cases with a known outcome | 15 of 74 (20.3 percent) | NICD Public Health Bulletin, 2020 |
| Severe respiratory illness patients with Legionella, 2012 to 2014 | 21 of 1 805 (1.2 percent), 4 of the 21 died | NICD sentinel surveillance (Wolter et al., 2016) |
| Community-acquired pneumonia linked to Legionella | Studies have suggested about 8 percent | NICD FAQ 2016, NIOH awareness material |
| Published community outbreak with an identified source | None | Published literature to date |
Put that beside Europe, where the ECDC reports 15 362 cases in 29 countries in 2024. South Africa notified 93 in close to three years, and the sentinel study authors say legionellosis is notifiable here but rarely reported. Many cases are likely treated as ordinary pneumonia and never named. For a hotel, a care centre or a food plant, the real risk is that the first time anyone looks hard at your water is during an investigation.
How is Legionnaires’ disease prevented?
The NICD’s guidance sets out the basics: store hot water above 60 °C, deliver it to taps above 50 °C, store cold water below 20 °C, and remove dead legs and low-flow areas. On a South African site that becomes a routine:
- Hot water stored at 60 °C or above and reaching outlets at 50 °C or more within one minute (HSE HSG274 Part 2), with thermostatic mixing valves where scalding is a risk.
- Cold water below 20 °C within two minutes of running, with no more than a day’s use in storage.
- Little-used outlets flushed weekly, and showerheads cleaned, descaled and disinfected quarterly.
- Cooling towers on a written scheme, with dip slides weekly and Legionella samples at least quarterly.
- Trained staff. The HBA Regulations, 2022 require training before possible exposure, with a refresher every year or at intervals the health and safety committee or representative recommends.
Behind the routine sits the paperwork the HBA Regulations ask for: a documented risk assessment by a competent person, an action plan, and written procedures and control protocols. ASC puts those into one water management plan, run by a named responsible person appointed in writing (see who is responsible for Legionella). Accommodation sites can start with our hotel and guesthouse checklist.
Responsible for a building where vulnerable people shower?
Legionella Responsible Person Training teaches the person in charge to assess the risk, write the plan and respond when someone falls ill, on a full hotel case and a frail care case. Ten hours, R2 950.
What happens when a case is linked to a building?
Legionellosis is a Category 2 notifiable medical condition: the doctor or laboratory that diagnoses it notifies within 7 days, not the employer. Two or more cases linked to one place within 12 months is a cluster, and municipal environmental health practitioners start a full environmental assessment, ideally within 24 hours (NICD). The site takes the suspected outlets out of use at once, but does not drain, flush or disinfect until the responsible person has agreed the next steps with the investigating EHP, so samples can be taken first. Sampling is covered in Legionella testing in South Africa and the legal duties in Legionella regulations in South Africa.
Frequently asked questions
What is Legionnaires’ disease?
Legionnaires’ disease is a severe pneumonia caused by Legionella bacteria, most often Legionella pneumophila serogroup 1. People catch it by breathing in fine water droplets from showers, hot tubs, cooling towers and similar sources. It is named after a 1976 outbreak at an American Legion convention.
What are the symptoms of Legionnaires’ disease?
The CDC lists cough, fever, headache, muscle aches and shortness of breath, sometimes with confusion, diarrhoea or nausea. Symptoms usually start 2 to 10 days after exposure. Because they look like any pneumonia, a doctor needs a chest X-ray and a urine or sputum test to confirm Legionella.
Is Legionnaires’ disease contagious?
As a rule, no. The CDC, HSE and WHO say it does not spread from person to person, and the NICD says it has never been documented in its experience. One probable exception is recorded, in Portugal in 2014. People catch it from contaminated water droplets, not from each other.
What is Pontiac fever?
Pontiac fever is the milder form of legionellosis: a flu-like illness with fever, muscle aches and headache but no pneumonia. It starts a few hours to 48 hours after exposure and usually lasts 2 to 5 days (WHO). Up to 95 percent of people exposed can fall ill.
How many cases of Legionnaires’ disease are there in South Africa?
The NICD recorded 93 notified cases from January 2018 to September 2020, 72 in the Western Cape, which the NICD puts down to more awareness and testing there. The true number is likely to be higher: the disease is notifiable but rarely reported, and studies have suggested about 8 percent of community-acquired pneumonia here is linked to Legionella.
Who is most at risk of Legionnaires’ disease?
People aged 50 or over, current and former smokers, and people with chronic lung disease, diabetes, cancer, kidney or liver failure or a weakened immune system (CDC). In South African surveillance, most patients with Legionella had HIV, TB or both. Healthcare-acquired cases are the deadliest, with about 1 in 4 dying (CDC).
Can you get Legionnaires’ disease from drinking water?
Not by drinking it normally. Water that goes into the stomach is not the route. You catch it by breathing in droplets or by aspiration, when water goes down the wrong way into the lungs. Showers, hot tubs, misters and cooling tower drift matter far more than a glass of water.
Make sure the people closest to the water know what to look for
Four hours for the team: where Legionella hides, the temperature numbers, flushing and what to report. Ten hours for the person who carries the duty, with a full hotel risk assessment and water management plan built in the course. Both are written for South African law and South African buildings.
Enrol in Awareness Training (R799) →Responsible Person course (R2 950)Self-paced, works on a phone. HPCSA CPD accredited. Certificate on passing.
Sources and further reading
- CDC: about Legionnaires’ disease
- WHO fact sheet: legionellosis
- NICD Public Health Bulletin (2020): notified Legionnaires’ disease
- Wolter et al. (2016), Legionella in severe respiratory illness, South Africa
- NICD recommendations for Legionnaires’ disease
- CDC MMWR: Legionnaires’ disease outbreaks, 2000 to 2014
- ECDC annual epidemiological report for 2024