Responding to shortages at healthcare facilities, CDC updated in April on recommended strategies for conserving supplies of N95 filtering facepiece respirators. The guidance suggests actions that healthcare employers can take when N95 FFR supplies are running low, and when no respirators are left. Possible administrative controls for coping with shortages of N95 FFRs include decreasing the length of hospital stays for medically stable patients with COVID-19 and temporarily suspending fit testing. In March, OSHA for annual fit testing for N95 FFRs. Strategies for preserving N95 FFRs when supplies are running low include using respirators beyond their manufacturer-designated shelf life, and using respirators approved under standards in other countries. The guidance includes a table identifying which respirators certified in other countries may be used in lieu of NIOSH-certified products. When no respirators remain, the guidance recommends excluding healthcare workers who are at higher risk for severe illness from contact with known or suspected COVID-19 patients, and designating healthcare workers who have recovered from COVID-19 to care for patients who have or may have contracted the disease. The guidance indicates that healthcare workers who have recovered from COVID-19 may have developed immunity but cautions that this has not yet been proven. Engineering controls that can be used for COVID-19 patients include creating expedient patient isolation rooms featuring carefully placed portable fans with high-efficiency particulate air (HEPA) filters to increase air-changes per hour. NIOSH describes the use of HEPA filtration systems for patient rooms on its . Another engineering control option is the use of .