Kawasaki Disease: The Fever That Must Not Be Missed

Most childhood fevers are viral and self-limiting — three or four miserable days, paracetamol, fluids, and they bounce back. Kawasaki disease is the one exception experienced paediatricians keep at the back of their mind, because the consequences of missing it are not "a longer cold" but coronary artery damage in early childhood.

It is not common — UK incidence is around 8–10 per 100,000 children under 5 — but the treatment is dramatically effective when given early, and dramatically less effective when given late. The job of any parent or GP is to think of it in time. The rest of the system handles it well.

It is named after Tomisaku Kawasaki, the Japanese paediatrician who first described it in 1967. It is more common in children of East Asian background but happens in every population.

Healthbooq (healthbooq.com) covers the important childhood illnesses, including the rare ones that matter.

What Kawasaki Disease Actually Is

A systemic vasculitis — inflammation of the small and medium-sized blood vessels throughout the body — affecting young children. The bit that matters medically is what it does to the coronary arteries. Without treatment, around 25% of children develop weakening of the coronary artery walls (aneurysms), which carry a lifetime risk of clotting, heart attack, and rupture.

It is not infectious — your child cannot catch it from another child, and you cannot catch it from your child. It clusters in seasons and small geographic outbreaks, suggesting an infectious trigger sitting on top of a genetic susceptibility, but no specific organism has been identified despite decades of looking. The best current model is "an aberrant immune response to a common trigger in genetically primed children."

Peak age is 6 months to 5 years, with the highest incidence around 12 to 18 months. Boys are affected slightly more than girls. It is rare under 3 months and uncommon over school age.

What It Looks Like

The classic picture is a young child who:

• Has had a high fever (38.5°C or above) for five days or more, often poorly responsive to paracetamol and ibuprofen
• Looks really unwell — out of proportion to anything you'd expect from a simple virus, miserable, irritable, off food, refusing to play
• Has some combination of the five "classic" features below

Diagnosis traditionally requires fever for ≥5 days plus 4 of the 5:

1. Bilateral red eyes (conjunctival injection). Both eyes red, but no pus, no crusting, no stickiness — the whites of the eyes look bloodshot rather than infected. This distinguishes it from bacterial conjunctivitis. The redness usually spares a small ring around the iris.

1. Red, cracked lips and a "strawberry tongue." Lips look raw and split. The tongue is bright red with prominent bumps (papillae), like the surface of a strawberry. The inside of the mouth is generally red.

1. Rash. Highly variable — flat red patches, raised bumps, large patches resembling measles. It is not blistery and not vesicular. It is on the trunk and limbs. A particularly suggestive sign is rash and redness around the genitals and nappy area early in the illness.

1. Hand and foot changes. In the acute phase, the palms and soles are red and the hands and feet are puffy and tense — a child who normally walks may refuse to bear weight. Around days 10–20, characteristic peeling starts at the fingertips and toes (peri-ungual peeling) — sometimes coming off in sheets like a sunburn.

1. One swollen lymph node in the neck. Usually on one side only, larger than 1.5 cm. This is the least consistent feature — about half of children show it.

You do not need all five. Fever ≥5 days plus four of those features is "complete" Kawasaki. Fever ≥5 days plus only two or three features, especially in a child who is otherwise unwell with no other diagnosis, is "incomplete" Kawasaki — and crucially, incomplete is not benign. Children with incomplete Kawasaki are diagnosed later on average, and have higher rates of coronary artery damage as a result. The advice for any child under 5 with fever lasting more than 5 days without a clear cause is the same: be seen, be properly assessed, do not leave it to the next call.

Children Who Don't Fit the Textbook

Two groups of children frequently present atypically:

• Babies under six months. Often have far fewer than four classic features, sometimes just persistent fever and poor feeding. Their incidence of coronary aneurysms when missed is the highest of any group. Any baby under six months with fever for five days and no source warrants formal evaluation including bloods and an echocardiogram.
• Older children. Past age 5, presentations can be subtle, with one or two features and a long fever.

In both groups, the diagnosis is missed when teams pattern-match to the classic toddler picture. Getting it right depends on the threshold being low.

What Bloods and Scans Show

No single test diagnoses Kawasaki disease. The picture is built from clinical features plus characteristic blood patterns:

• CRP and ESR are usually high (often very high — CRP >100, ESR >50)
• White cell count is up with a neutrophil predominance
• Platelets rise dramatically into the second week of illness — often into the 600–1000 range. This is one of the more specific features.
• Mild anaemia is common
• Liver enzymes (ALT) are often modestly elevated
• Sterile pyuria (white cells in the urine without infection) is a classic clue

An echocardiogram is part of the assessment at diagnosis — to look at the coronary arteries directly and provide a baseline for follow-up — and is repeated at 2 weeks and 6–8 weeks. Coronary changes can develop or progress over the first weeks even with treatment.

Treatment

The treatment is one of medicine's success stories. A single high-dose infusion of intravenous immunoglobulin (IVIG) at 2 g/kg, given over 10–12 hours, combined with aspirin, brings down the rate of coronary artery aneurysms from around 25% to under 5% when given within the first 10 days of illness. The earlier within that window, the better.

Aspirin is used in two phases: high anti-inflammatory doses while fever continues, then dropped to a low antiplatelet dose once the child has been afebrile for 48 hours, continued for at least 6–8 weeks until the follow-up echo is clear.

About 10–15% of children don't respond to the first IVIG dose (fever returns within 36 hours). They are given a second dose, sometimes with corticosteroids or infliximab. This is managed by paediatric cardiology or paediatric infectious disease teams.

Treatment is in hospital. In the UK, any suspected case is admitted, started on IVIG promptly, and reviewed by a paediatric cardiologist.

What Parents Actually Need to Do

This is a "see your GP or A&E in time" disease, not a "treat at home" one. The practical message is short:

• Fever in a young child for 5 days or more without a clear diagnosis = be seen. Not necessarily 999, but the same day. NHS 111, GP same-day, or A&E if the child looks really unwell.
• Mention the features explicitly if any are present: "she has had fever for five days, both eyes are red without pus, her tongue looks red and bumpy, her lips are cracked, she has a rash and her hands look swollen." Those words switch a triage call from "another viral fever" to "rule out Kawasaki disease."
• Don't wait for all five features. Two or three plus prolonged fever is enough to act on.
• Don't let "but the swab was negative for strep" reassure you. Plenty of children have an irrelevant viral PCR positive while developing Kawasaki disease at the same time. The fever pattern and the clinical picture are what matter.

After the Acute Illness

Children whose 6–8 week echocardiogram is normal can usually be discharged from cardiology follow-up entirely — they have effectively had a serious illness with no lasting consequences.

Children who develop coronary artery aneurysms have ongoing cardiology follow-up — sometimes lifelong — including antiplatelet or anticoagulant medication, advice on physical activity (most can do most things), and surveillance for cardiovascular risk into adulthood.

Recurrence happens in around 1–3% of children. A child who has had Kawasaki disease and develops a fresh prolonged fever needs to be reviewed again with that history specifically in mind.

The headline for parents: think of it, mention it by name when ringing the GP, don't accept "it's just a virus" if the fever is into day 5 or 6 and the child looks miserable. Almost everything else, the system does well.

Kawasaki disease is the rare cause of fever that paediatricians genuinely lose sleep over: a feverish toddler who looks generally unwell for five days or more, with red eyes, a strawberry-red tongue, cracked lips, a rash, swollen hands or feet, sometimes a swollen neck gland on one side. Untreated, around 1 in 4 children develop coronary artery aneurysms — a real risk of heart attack in early childhood. Treated within the first 10 days with IVIG and aspirin, the risk drops below 1 in 20. The single rule worth knowing: a child under 5 with fever lasting more than 5 days without a clear diagnosis needs to be seen, today, and Kawasaki should be on the list.