Yes, a small number of cases could go unnoticed. But you were talking about large clusters. Say 100 people are infected and 15 turn up at hospital with difficul

Yes, a small number of cases could go unnoticed. But you were talking about large clusters. Say 100 people are infected and 15 turn up at hospital with difficulty breathing. For at least one of them, a doctor is going to take a history and notice the characteristic progression (this disease is the most famous disease in the world right now), then report it to their health authority. The large % of cases that require hospitalisation is a terrifying aspect of COVID-19, but it does increase the chance of detection.