The lack of follow up is indeed rather frustrating. On the plus side, the article reports that they kept the people in quarantine 8-12 days after the testing round. From other sources on the Web, "on average symptoms appear after 5 days and most people with symptoms had them by day 12". While the study has probably accounted for most of the symptomatic cases, a 30 day follow up would be of great value, including to validate the incubation period estimations.