Other factors that have classically increased suspicion are winter/early spring presentation in North America, male gender (1.5:1 ratio to females), and Asian (particularly Japanese) ancestry. The importance of genetics was initially based on epidemiology (Japan/Asian risk) but lately has been further associated with six gene polymorphisms. However, molecular genetic testing is not currently a practical tool.
Clinical scenarios that also should raise suspicion include less-than-6-month-old infants with prolonged fever/irritability (may be the only clinical manifestations of KD) and children over 4 years old who more often may have incomplete KD. Both groups have higher prevalence of coronary artery abnormalities. Other high suspicion scenarios include prolonged fever with unexplained/culture-negative shock, or antibiotic treatment failure for cervical adenitis or retro/parapharyngeal phlegmon. Consultation with or referral to a regional KD expert may be needed.
Fuzzy KD math
Current guidelines list an exception to the 5-day fever requirement in that only 4 days of fever are needed with four or more principal clinical features, particularly when hand and feet findings exist. Some call this the “4X4 exception.” Then there is a sub-caveat: “Experienced clinicians who have treated many patients with KD may establish the diagnosis with 3 days of fever in rare cases.”1