Table 1 Inclusion criteria and definitions

• Meet modified Marshall criteria [9]:

I. Regularly recurring fevers with an early age of onset (<  5 years of age)

II. Constitutional symptoms in the absence of upper respiratory infection with ≥ 1 of the following clinical signs:

a). Aphthous stomatitis, b) Cervical lymphadenitis, c) Pharyngitis

III. Exclusion of cyclic neutropenia

IV. Completely asymptomatic interval between episodes

V. Normal growth and development

N.B. In clinical practice, cyclic neutropenia was often excluded on clinical grounds.

and:

• Duration of episodes < 7 days

• No atypical features

Meet modified Marshall criteria

and have at least one atypical feature, i.e.

• length of fever episodes ≥ 7 days

• diarrhea

• chest pain

• skin rash

• arthritis

• severe abdominal pain

• sensorineural hearing impairment

• conjunctivitis

• periorbital edema

• cold- or exercise-triggered episodes

and not suspected of having another AID, based on expert opinion guided by the clinical classification criteria for monogenic AID [10]

PFAPA without atypical features but with late onset:

PFAPA with atypical features and with late onset:

Meet all the criteria stated above, except that the onset of symptoms occurred at ≥ 5 years of age

As stated above but with symptom onset at ≥ 5 years of age