Construction of easily comprehensible case definitions using Boolean operators
| Case definitions can contain Boolean logical operators such as AND, OR and AT LEAST (see supplementary material S1 for examples of international case definitions in current use) | |
| Symptom groups | Referred to in text as |
| fever, cough, anosmia | Canonical symptoms (CS) |
| headache, sore throat, muscle aches, appetite loss | Early-predictors (EP) |
| The EP were each combined individually with the CS using an “OR” operator | Referred to in text as |
| fever OR cough OR anosmia OR headache | CS or headache |
| fever OR cough OR anosmia OR sore throat | CS or sore throat |
| fever OR cough OR anosmia OR muscle aches | CS or muscle aches |
| fever OR cough OR anosmia OR appetite loss | CS or appetite loss |
| The EP were all combined together with the CS using “AT LEAST” and “OR” operators | Referred to in text as |
| fever OR cough OR anosmia OR AT LEAST 1 of headache, sore throat, muscle aches and appetite loss | ≥1 of the CS, or ≥1 of the EP |
| fever OR cough OR anosmia OR AT LEAST 2 of headache, sore throat, muscle aches and appetite loss | ≥1 of the CS, or ≥2 of the EP |
| fever OR cough OR anosmia OR AT LEAST 3 of headache, sore throat, muscle aches and appetite loss | ≥1 of the CS, or ≥3 of the EP |
| fever OR cough OR anosmia OR AT LEAST 4 of headache, sore throat, muscle aches and appetite loss | ≥1 of the CS, or ≥4 of the EP |