The CDC line list dataset from the USA provides 12 metadata fields for each patient. No unique ID is provided per patient. The date used as the date of confirmation is ‘cdc_case_earliest_dt’ which is the best available date from the set of dates related to illness/specimen collection (i.e. ‘pos_spec_dt’) or the date received by the CDC (i.e. ‘cdc_report_dt’). This ensures the date variable has optimized completeness, as the logic of ‘cdc_case_earliest_dt’ is to use the non-null date of one variable when the other is null and to use the earliest valid date when both dates are available. If no date is available then it is left blank. Although the earliest reported COVID-19 case date for the USA is the 20th of January 2020, the dataset includes 3175 cases reported between the 1st and the 20th of January 2020. 

The CDC dataset contains cases which are either a ‘Probable Case’ or a ‘Laboratory-confirmed case’; we only consider the laboratory confirmed cases as confirmed and do not ingest any probable cases. The CDC laboratory criteria for diagnosis found here describes a probable case as meeting the clinical criteria for severe respiratory illness and the epidemiological criteria for likely exposure to SARS-CoV-2. A confirmed case is a clinically compatible illness that is laboratory confirmed. 

When a variable is coded to the value ‘Unknown’, jurisdictions have specified in the case data submitted to the CDC that the value is unknown. When it is ‘Missing’, the jurisdiction did not provide a value to the CDC. When the value is ‘NA’ it has been suppressed as part of privacy protections. Data cells are suppressed for low frequency (<5) records and indirect identifiers. Suppression includes rare combinations of demographic characteristics (sex, age group, race/ethnicity). The age group categorizations were populated by the CDC using the age value that was reported on the case report form. Date of birth was used to fill in missing/unknown age values using the difference in time between date of birth and onset date. If more than race was reported, race was categorized into multiple/other races.

One of the major limitations of this dataset is the lack of geographic information; for this reason every case is geo-located to the centroid of the USA. The CDC does provide a dataset with geographic information to the county level, which also includes information about known exposure, symptom status, and process through which the case was identified (e.g. contact tracing). This dataset, however, only provides a case confirmation date to the closest month.