As countries in Europe gradually relaxed lockdown restrictions after the first wave, test-trace-isolate strategies became critical to maintain COVID-19 viral activity at low levels1,2. Reviewing their shortcomings can provide elements to consider in light of the second wave currently underway in Europe. Here we estimate the rate of detection of COVID-19 symptomatic cases in France after lockdown through the use of virological3 and participatory syndromic4 surveillance data coupled with mathematical transmission models calibrated to regional hospitalizations2. Our findings indicate that around 90,000 incident symptomatic infections, corresponding to 9 out 10 cases, were not ascertained by the surveillance system in the first 7 weeks following lockdown from May 11 to June 28 2020, although the test positivity rate did not exceed WHO recommendations (5%)5. The median detection rate increased from 7% [6-8]% to 38% [35-44]% over time, with large regional variations, owing to a strengthening of the system as well as a decrease of epidemic activity. According to participatory surveillance data, only 31% of individuals with COVID-19-like symptoms consulted a doctor in the study period. This suggests that large numbers of symptomatic COVID-19 cases did not seek medical advice despite recommendations, as confirmed by serological studies6,7. Encouraging awareness and same-day healthcare-seeking behavior in suspect cases is critical to improve detection. However, the capacity of the system remained insufficient even at the low levels of viral circulation achieved after lockdown, and was predicted to deteriorate rapidly with increasing epidemic activity. Substantially more aggressive, targeted, and efficient testing with easier access is required to act as a pandemic-fighting tool. Testing strategy will be once again of critical value to lift current restrictive measures in Europe and avoid a third wave.

中文翻译：

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法国对 COVID-19 病例的检测不足威胁到流行病控制

随着欧洲国家在第一波疫情之后逐渐放松封锁限制，测试追踪隔离策略对于将 COVID-19 病毒活动保持在低水平变得至关重要1,2。鉴于欧洲目前正在进行的第二波疫情，审查它们的缺点可以提供需要考虑的因素。在这里，我们通过使用病毒学 3 和参与式综合征 4 监测数据以及根据区域住院情况校准的数学传输模型来估计法国封锁后 COVID-19 有症状病例的检出率。我们的研究结果表明，在 2020 年 5 月 11 日至 6 月 28 日封锁后的前 7 周内，监测系统未确定大约 90,000 例有症状的感染事件，对应于十分之九的病例，尽管检测阳性率没有超过世卫组织的建议（5%）5。随着时间的推移，中位检测率从 7% [6-8]% 增加到 38% [35-44]%，由于系统加强以及流行活动减少，区域差异较大。根据参与式监测数据，在研究期间，只有 31% 的有 COVID-19 样症状的人咨询了医生。这表明，血清学研究证实了大量有症状的 COVID-19 病例，尽管提出了建议，但并未寻求医疗建议6,7。鼓励对疑似病例的认识和当日就医行为对于提高发现率至关重要。然而，即使在锁定后病毒传播水平较低的情况下，该系统的容量仍然不足，并且预计会随着流行病活动的增加而迅速恶化。作为一种抗击大流行的工具，需要更积极、更有针对性和更有效的测试，并且更容易访问。测试策略将再次具有关键价值，以解除欧洲目前的限制措施并避免第三波。