(AP) — The long-delayed effort to ramp up screening for the coronavirus in the U.S. is facing a new challenge: critical shortages of laboratory supplies. Public health officials warn of dwindling levels of testing chemicals, swabs and other testing needs. Some labs have had to cut back or halt testing due to lack of supplies. Wide scale testing is a critical part of containing infectious diseases. But a series of stumbles have left the U.S. weeks trailing behind most other developed countries. Now laboratory workers worry the introduction of drive-thru testing and mass screening will further pressure supplies.