Distribution of prespecified PCC definition sources used in included studies by age group, n=291 studies
| Definition source | Total (n=291) | Paediatric (n=23) | Adult (n=221) | Mixed (n=41) | Not reported (n=6) |
| N (%) | N (%) | N (%) | N (%) | N (%) | |
| Author definition | 150 (51.5) | 10 (43.5) | 119 (53.1) | 18 (43.9) | 3 (50.0) |
| Based on another referenced study | 37 (12.6) | 4 (17.4) | 24 (10.7) | 9 (22.5) | 0 (0) |
| CDC | 7 (2.4) | 0 (0) | 6 (2.7) | 1 (2.5) | 0 (0) |
| ICD-10 U09.9* | 5 (1.7) | 1 (4.3) | 3 (1.3) | 2 (4.9) | 0 (0) |
| ICD-10 codes† | 1 (0.3) | 1 (4.3) | 0 (0) | 0 (0) | 0 (0) |
| National guidelines‡ | 1 (0.7) | 0 (0) | 1 (0.4) | 0 (0.0) | 0 (0) |
| NICE | 18 (6.2) | 4 (17.4) | 14 (6.3) | 0 (0) | 0 (0) |
| Not prespecified by author§ | 53 (18.1) | 0 (0) | 38 (17.2) | 8 (17.5) | 3 (50.0) |
| WHO | 22 (7.5) | 3 (13.0) | 16 (7.1) | 3 (7.5) | 0 (0) |
*Includes studies explicitly reporting ICD-10 U09.9 diagnoses, and a mixed adult and paediatric study that used a Danish equivalent of ICD-10 U09.9 diagnostic code (DB948A implemented 1 April 2020 by the Danish Board of Health.64
†A literature review65 which analysed ICD-10 codes by clustering 121 syndromic, and systemic symptoms and conditions, and medication uses (therapeutic classes) reported for postacute sequelae of COVID-19, to predict clinically relevant symptoms.65
‡Adult study used definition from National Comprehensive Guidelines for Management of Post-COVID Sequelae for India.66
§Refers to included studies that prospectively followed patients with confirmed acute SARS-CoV-2 to investigate and characterise persistent symptoms.
CDC, Centers for Disease Control and Prevention; ICD-10-CM, International Classification of Diseases, Tenth Revision, Clinical Modification; NA, not applicable; NICE, National Institute for Health and Care Excellence.;