Legionnaires' disease

This is a severe pneumonia you catch from water rather than from another person. The bacterium Legionella multiplies in lukewarm pipework, hot water cylinders, hot tubs and building cooling systems, and reaches the lungs in the fine spray that people breathe in without noticing.

It is not a common illness, but it is worth knowing about for one reason: the antibiotics usually chosen first for pneumonia have no effect on Legionella. Whether the illness stays mild or turns severe often comes down to whether the doctor thought of it in time, and the person best placed to give that hint is the patient, by recalling where they have been over the past fortnight.

Where Legionella lives and how it reaches the lungs

Legionella is an ordinary inhabitant of fresh water and damp soil, and out in nature it does no harm. Trouble starts wherever water sits lukewarm for long periods: somewhere between twenty and forty-five degrees the bacterium multiplies happily, and the scale and slimy film inside pipework give it shelter.

Infection happens only when water is broken into a cloud of tiny droplets that can be breathed in. Hence the list of usual suspects:

• showers and taps left unused for a while: the house after a holiday, an empty hotel room, the changing room of a pool shut for the summer;
• hot tubs, spa baths and whirlpool pools, particularly ones in public use;
• cooling towers on the roofs of hotels, hospitals and shopping centres: the mist they release travels hundreds of metres and catches passers-by who never went inside;
• humidifiers, ornamental fountains, garden sprinklers, pressure washers;
• less often, dental units and breathing equipment rinsed with tap water.

What not to worry about matters just as much. The illness practically never passes from person to person, so there is no need to keep away from someone who has it. Drinking water containing the bacterium does not infect you: it has to enter the airway, not the stomach. Ponds, lakes and rivers pose no risk. The danger is not water as such, but warm water turned into mist.

Between breathing it in and the first symptoms there are usually two to ten days, occasionally up to a fortnight. So the thing to think back over is not yesterday but the last trip away.

What it feels like

It begins like flu: exhaustion, aching muscles, headache, no appetite. Within a day or two the temperature climbs high, often with shivering, and a cough appears, dry at first and later bringing up small amounts of phlegm, sometimes streaked with blood. Breathing becomes harder and the chest hurts on a deep breath.

Some features are unusual for ordinary pneumonia, and those are exactly the ones that point towards Legionella:

• diarrhoea, nausea, vomiting or tummy pain from the first days;
• confusion, slowed responses, unusual drowsiness — in older people this can be the only visible change;
• a very high temperature with a relatively slow pulse;
• severe headache that ordinary painkillers do not touch.

Call an ambulance straight away if the person is short of breath at rest or cannot finish a sentence, if the lips turn blue, if they do not come round properly and fail to recognise those around them, if the skin turns cold and clammy, or if they have passed no urine for many hours. The single European emergency number 112 works in Spain, Italy, Portugal, Poland and Ukraine.

If a high temperature with cough and breathlessness persists but the situation is not critical, see a doctor the same day. With this illness a week of waiting is a very long time.

Pontiac fever, the mild twin

The same bacterium sometimes causes something quite different: within hours of contact, at most two or three days, come fever, shivering, headache and aching limbs, much like flu but without any pneumonia. There is barely a cough, the chest X-ray is clear, everything settles by itself in two to five days and antibiotics are not needed.

It is worth knowing about for another reason: it strikes several people who were in the same building at once, and usually means there is a source nearby that will sooner or later give someone genuine pneumonia.

Who fares worse

Most people who breathe the bacterium in never become ill at all. The risk rises when several circumstances coincide:

• smoking, the most avoidable of them: smoke disables the airway's self-cleaning mechanism;
• middle and older age; the illness is rare in children;
• chronic lung conditions such as obstructive lung disease, emphysema, scarring from old tuberculosis;
• diabetes, kidney or liver failure, heavy drinking;
• weakened defences: cancer treatment, steroids and other medicines that damp down immunity, an organ transplant;
• recent surgery or a stay in hospital.

Men fall ill roughly three times as often as women, and the reason is not how the body is built but smoking and the kind of work people do.

How it is identified

A chest X-ray cannot tell this pneumonia from any other: the picture varies. The diagnosis is made in the laboratory. The quickest answer comes from a urine test for the bacterial antigen, with a result the same day. It has one significant weakness: it picks up only the commonest variety of the organism, so a negative result rules nothing out, and if the picture still points to Legionella, sputum culture and genetic testing are added.

Ordinary blood tests help too: sodium often falls, liver readings and a muscle enzyme rise, and the kidneys suffer. On their own none of these proves anything; together they form a recognisable pattern.

At the appointment, be sure to say where you have been over the past fortnight: a hotel, a cruise, a spa, a health resort, a building site, a return to a home left empty for months. That one sentence changes the course of treatment faster than any test.

How it is treated

Treatment is with antibiotics, and here the choice matters as much as the speed. Legionella lives inside cells, so penicillins and cephalosporins — the usual opening move in pneumonia — never reach it. Two groups do work: macrolides and respiratory fluoroquinolones. Where suspicion is strong they are started without waiting for laboratory confirmation.

Severe cases are treated in hospital with the drug given into a vein, alongside whatever the situation calls for: oxygen, mechanical support for breathing if respiratory failure worsens, dialysis if the kidneys fail. Once the fever settles, treatment switches to tablets and finishes at home. The course runs from one to three weeks, longer after a severe illness or with weakened immunity, and it has to be completed in full even if there is clear improvement within three days.

Most people recover completely, but slowly: tiredness and breathlessness on exertion last for weeks and sometimes months, and that is normal convalescence rather than a complication. The illness nonetheless remains dangerous — around one in ten of those affected dies, and almost always these are the people whose treatment started late.

What can be done to avoid it

There is no vaccine, so all the protection lies in how water is handled.

• Coming back to the house after a long absence, run both the hot and the cold taps for several minutes. It is better to take the shower head off the hose and put it in a bucket so as not to raise a spray, and to leave the room while it runs.
• Keep the water in the cylinder genuinely hot, no lower than sixty degrees, and the cold water genuinely cold. The lukewarm middle ground is exactly what the bacterium is waiting for. If there are children or older people in the house, fit a temperature limiter at the tap rather than turning the cylinder down.
• Descale shower heads and tap aerators every few months.
• Drain the garden hose and do not leave it lying full in the sun.
• Service a home hot tub as the instructions say: without working filtration and disinfection it becomes a perfect incubator.
• Fill humidifiers and inhalation devices with boiled or sterile water, never straight from the tap.
• Stopping smoking is the single most effective item on this list, if it applies to you.

One more thing: if you fell ill after a hotel, a cruise or a spa, tell your doctor and report it to the establishment itself and to the local public health service. One source traced spares the illness to dozens of people who will arrive there after you.

Online consultation

A remote appointment is useful at two points. Early on, when fever and a cough follow a trip away: the doctor can judge how worrying the picture is, suggest which tests to ask for and what to mention without fail at the face-to-face visit so that Legionella is not overlooked. And after recovery, when the antibiotics have finished but tiredness and breathlessness persist: the conversation is then about what still counts as normal convalescence and what calls for further investigation.

Be seen in person and without delay if breathing becomes hard at rest, if confusion sets in, if the lips turn blue or blood pressure drops sharply. That needs an examination and an X-ray, not a message.

This material is for information only and does not replace medical advice.