Mass testing with rapid tests that detect viral antigen has been proposed to identify contagious individuals and thereby control the current SARS-CoV-2 pandemic (1). In Germany, alongside testing in physicians’ offices, commercial test centers were opened and kits for self-testing were made available. Because the positive predictive value (PPV; a truly positive test result confirming infection) of rapid tests may be insufficient at times of low infection activity, the present study aimed to determine the value of rapid tests by the analysis of data on PCR tests performed to confirm positive rapid test results in physicians’ offices and test centers between January 2021 and February 2022.
Figure.
Rapid tests confirmed by PCR (bars) versus 7-day incidence in Berlin, Germany (curve) for January 2021 to February 2022. The numbers in parentheses after each month show the total PCR tests performed for confirmation of positive rapid test results.
Footnotes
Conflict of interest statement
Dr. Müller is chair of the association Accredited Laboratories in Medicine (Akkreditierte Labore in der Medizin e. V.).
The remaining authors declare that no conflict of interest exists.
Methods
Starting in January 2021, our electronic order entry system included an additional step to request “confirmation of a positive rapid test.” All senders not using the order entry system were asked to provide this information on their referral form. These data were extracted from our laboratory information system for the period January 2021 to February 2022 for the area of Greater Berlin. The PCR tests carried out in our laboratory make up about 10% of all such tests performed by the around 20 laboratories in Berlin.
Median monthly 7-day incidences of COVID-19 were extracted from the data provided by the Berlin State Office for Health and Social Affairs. The proportions of rapid tests confirmed by PCR (corresponding to the PPV) were calculated with 95% confidence intervals (95% CI) and the data were statistically analyzed by means of the two-tailed chi-square test.
Results
Of 14 572 samples submitted by 406 physicians’ offices and 53 test centers with the request for “confirmation of positive rapid test,” 11 742 positive rapid test results (80.6%) were confirmed by PCR (table). The percentage of samples confirmed as positive was lower for physicians’ offices than for test centers. More than 100 samples were submitted by each of 13 test centers (accounting for 88.2% of all test center samples) and 22 physicians’ offices (amounting to 48.6% of samples from this source); for both groups, the proportions of confirmed rapid tests corresponded to the numbers of samples submitted (table).
Table. PCR results of samples submitted by physicians’ offices versus test centers between January 2021 and February 2022 for confirmation of positive rapid tests.
| Source of samples | Number of PCR samples | Samples with positive PCR result | Confirmed rapid tests% [95% CI] |
| Physicians’ offices | |||
| All (n = 406) | 7843 | 5926 | 75.6 [74.6; 76.5] |
| < 100 samples (n = 384) | 4034 | 2936 | 72.8 [71.4; 74.1] |
| ≥ 100 samples (n = 22) | 3809 | 2990 | 78.5 [77.2; 79.8] |
| Test centers | |||
| All (n = 53) | 6729 | 5816 | 86.4 [85.6; 87.2] |
| < 100 samples (n = 40) | 796 | 597 | 74.9 [71.9; 77.9] |
| ≥ 100 samples (n = 13) | 5933 | 5219 | 88.0 [87.1; 88.8] |
| Total | 14 572 | 11 742 | 80.6 [79.9; 81.2] |
PCR, Polymerase chain reaction; 95% CI, 95% confidence interval
In the year 2021, when the viral variants Alpha (B.1.1.7) and Delta (B.1.617.2) predominated and there were 7-day incidences of 13.05 to 338.10, 2870 of 4484 rapid test samples were confirmed (64.0% [62.6; 65.4]; Figure); the proportion of rapid test results confirmed was higher for physicians’ offices than for test centers (physicians’ offices: 65.1% [63.5; 66.6], test centers: 59.9% [56.7; 63.0]). In January/February 2022, however, with the Omicron variant (B.1.1.529) predominant and 7-day incidences >1000, the overall proportion of rapid tests confirmed was 87.9% [87.3; 88.6]. The proportion confirmed was now lower for samples from physicians’ offices than for those from test centers (physicians’ offices: 84.2% [83.1; 85.3], test centers: 90.7% [89.9; 91.4]), independently of test centers that exclusively submitted samples in 2022 (data not shown) and, notably, also lower in physicians’ office samples from symptomatic patients (n = 2126), who were identified by the billing category (85.6% [84.1–87.1]).
Discussion
Our data correspond to an average PPV of 0.64 for the year 2021 and 0.88 for early 2022, in parallel with the infection incidence, as would be expected. A PPV of 0.53 for May 2021 was reported for Cologne, Germany, together with an estimate of the damage to the economy caused by false-positive rapid tests (2).
Only for 2021 did we observe more frequent confirmation of rapid tests in samples submitted by physicians’ offices, where staff are experienced in collection of upper respiratory swabs. The opposite (even compared with symptomatic patients in physicians’ offices) was found for January/February 2022. This may indicate that increasing numbers of symptomatic COVID-19 patients were seeking help in non-medical facilities.
Rapid tests were originally introduced to detect SARS-CoV-2-positive individuals. Later, the idea arose that “rapid test negativity” might confer eligibility to attend events, etc. Owing to the study design, we can make no statement regarding the rate of false-negative rapid tests. However, previous studies on rapid tests in asymptomatic students and in children have indicated sensitivity of 20% and 56.2%, respectively (3, 4), below the 80% sensitivity demanded by the European Centre for Disease Prevention and Control (ECDC) and the World Health Organization (WHO) (1). Low sensitivity, however, can be compensated only by high frequency of testing and swift provision of results (5). Further limitations of our study are the lack of information on the source of rapid tests (samples obtained at the physicians’ offices/test centers or self-testing), the reasons for the rapid tests, and the rapid test brands used.
Conclusion
Our data indicate that SARS-CoV-2-specific rapid tests without subsequent PCR confirmation should be used primarily at times of high incidence and on the basis of future control strategies. Symptomatic patients, however, should be seen exclusively in physicians’ offices, in order to initiate antiviral therapy, if indicated, as early as possible.
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