Results of the search
The search yielded 10,965 records after removing duplicates. The first selection resulted in 658 records that were potentially eligible for this review on signs and symptoms. After screening on title and abstract, we excluded 457 records, leaving 201 to be assessed on full text. Of these, we included 16 studies in this review. The reasons for excluding 185 records are listed in the PRISMA flow chart (see Figure 1; Moher 2009).
1  Flow diagram Two studies reported on the same cases while using a different control group (Chen X 2020; Yang 2020d). Chen X 2020 used a concurrent control group of pneumonia cases negative for SARS‐CoV‐2 on PCR testing but Yang 2020d used a historic control group of influenza pneumonia patients. For this reason we only included the Chen X 2020 results in the analyses.
One study reported a study that included a derivation and validation part for the development of a prediction rule (Song 2020b). The two parts are identical in set‐up and only differ in respect to the time of data collection, that is, the derivation part recruited participants up to 5 February 2020 and the validation part recruited participants from 6 February 2020 onwards. As a result, we consider this to be one study and have entered all data on signs and symptoms as such.
Four studies were conducted in the USA, all other studies were from China. A summary of the main study characteristics can be found in Table 3.
2  Summary of study characteristics
Study ID   Target condition   Sample size   Prevalence   Setting   Population   Design   Reference standard
Ai 2020a  COVID‐19 pneumonia  53  38%  Hospital inpatientsa  Patients hospitalised with pneumonia diagnosed by imaging  Cross‐sectional  PCR on nasopharyngeal swabs
Chen X 2020  COVID‐19 pneumonia  136  Not applicable  Hospital inpatientsa  Patients admitted with pneumonia  Cases selected cross‐sectionally in 5 hospitals, non‐cases from 1 hospital only  PCR, samples not specified
Cheng 2020a  COVID‐19 pneumonia  33  33%  Hospital outpatients  Patients presenting to a fever observation department with pneumonia  Cross‐sectional  PCR on throat swabs
Feng 2020a  COVID‐19 pneumonia  132  5%  Emergency department  Patients presenting to fever clinic of emergency department  Cross‐sectional  PCR on throat swabs
Liang 2020  COVID‐19 pneumonia  88  24%  Hospital outpatients  Patients with pneumonia and presenting to fever clinic  Cross‐sectional  PCR, sample not specified; conducted after panel discussion
Nobel 2020  COVID‐19 disease  516  Not applicable  Hospital outpatients  Patients who underwent SARS‐CoV‐2 testing with intent to hospitalise or in essential personnel  Case‐control  PCR on nasopharyngeal swabs
Peng 2020a  COVID‐19 disease  86  13%  Hospital outpatients  Patients clinically suspected and referred for testing  Cross‐sectional  PCR on nasopharyngeal swabs
Rentsch 2020  COVID‐19 disease  3789  15%  Unclear  Patients tested for SARS‐CoV‐2 in the Veterans Affairs Cohort born between 1945 and 1965  Cross‐sectional  PCR on nasopharyngeal swabs
Song 2020b  COVID‐19 disease  399  7%  Hospital outpatients  Patients tested for SARS‐CoV‐2  Cross‐sectional  PCR on sputum samples
Sun 2020a  COVID‐19 disease  788  7%  Hospital outpatients  Patients presenting to testing centre, either self‐referred, referred from primary care or at‐risk cases identified by national contact tracing  Cross‐sectional  PCR on sputum, endotracheal aspirate, nasopharyngeal swabs or throat swabs
Tolia 2020  COVID‐19 disease  283  10%  Emergency department  Patients presenting with symptoms, travel history, risk factors or healthcare workers  Cross‐sectional  PCR on nasopharyngeal swabs
Wee 2020  COVID‐19 disease  870  18%  Emergency department  Patients presenting with respiratory symptoms or travel history  Cross‐sectional  PCR on oropharyngeal swabs
Yan 2020a  COVID‐19 disease  262  23%  Hospital outpatient  Patients presenting hospital for SARS‐CoV‐2 testing, not otherwise specified  Internet survey after presentation  PCR, samples not specified
Yang 2020d  COVID‐19 pneumonia  121  Not applicable  Hospital inpatientsa  Patient with pneumonia from SARS‐CoV‐2 and patients with pneumonia from influenza in 2015‐2019  Case‐control  PCR, samples not specified
Zhao 2020a  COVID‐19 pneumonia  34  Not applicable  Hospital inpatientsa  Patients with pneumonia and admitted to hospital  Case‐control  PCR on throat or sputum swabs
Zhu 2020b  COVID‐19 disease  116  28%  Emergency department  Patients suspected of SARS‐CoV‐2 and presenting to the emergency department  Cross‐sectional  PCR, samples not specified
PCR: polymerase chain reaction; SARS‐CoV‐2: severe acute respiratory syndrome coronavirus 2
a'Hospital inpatients' refers to studies that recruited patients admitted to hospital with COVID‐19 disease and in whom the signs and symptoms were assessed on admission.