Surveys to check the prevalence of coronavirus among the general population of Delhi will now be held every month, the state's health minister Satyendar Jain said today, announcing the beginning of the first of this series of surveys from August 1 to 4. The decision of the Delhi government came as the numbers of infected people dropped way below the last few weeks' average of 2,000, but a sero-survey indicated that at least one in five persons in Delhi had contracted the disease. The survey also indicated also indicated that a large number of infected persons remained asymptomatic, increasing the chances of the spread.