SARS transmission among protected HCWs puzzling

CDC researchers, HCWs in Toronto wearing N-95s

Hospitals acted to improve their respiratory protection programs as new questions surfaced about protections of health care workers from severe acute respiratory syndrome (SARS). When respirators are used for SARS or any infectious disease other than tuberculosis, health care workers must be fit-tested annually, according to the U.S. Occupational Safety and Health Administration (OSHA).

Respirator use and other precautions also came under scrutiny when an infection control expert from the Centers for Disease Control and Prevention (CDC) developed possible symptoms of SARS in Taiwan. Taiwan, which suffered from numerous hospital-based outbreaks and had more than 585 cases, has been struggling to control SARS. The investigator had been fit-tested to use an N95 and wore the same protective equipment that CDC employees use when encountering infectious diseases, such as Ebola, CDC director Julie Gerberding, MD, said in a press briefing.

CDC investigators retraced his activities in the days before he developed a fever and slight cough in an effort to trace his exposure, although Gerberding noted, "it may be that we’ll never exactly know when or where his exposure occurred," if he actually has SARS. Meanwhile, a different CDC team continued to study the transmission of SARS to protected workers in Toronto hospitals.

Was there a breach in infection control? Or is an even higher level of protection needed? Gerberding said CDC will "continue to look hard" at whether infection control precautions must be changed. But she also noted, "You have to be 100% compliant in order to be absolutely certain that there isn’t an inadvertent airborne exposure."

Hospitals already are scrambling to beef up their respiratory protection programs. Some are adding to the number of employees who have been fit-tested to wear N-95s. The OSHA respiratory protection standard (1910.34) requires annual fit-testing.

"The misinterpretation out there is that we require fit-testing for all employees in a facility," says Amber Hogan, industrial hygienist in OSHA’s Office of Health Enforcement. "We only require fit-testing for those employees who have exposure or potential exposure to those patients who have SARS."

She suggests designating clinicians in some departments, such as radiology or pediatrics, as part of a SARS care team and fit-testing those workers — but not everyone in the department. Hogan also noted that there likely would be an overlap between those fit-tested to care for TB patients and those who might encounter a SARS patient.

Some hospitals have turned to powered air-purifying respirators (PAPRs) as an alternative protection. PAPRs do not have to be fit-tested and can be used by more than one employee.

One thing is clear about SARS: Worldwide, hospitals have been a major focus of transmission.

In Taiwan, a six-day delay in diagnosing a hospital laundry worker with SARS led to unprotected exposure of about 10,000 patients and visitors and 930 employees. From that one chain of exposure, 137 people developed symptoms and are "probable" cases of SARS; 45 of them (33%) were hospital workers.1

Elsewhere, hospital workers have been among the most prevalent victims. In Hong Kong, 85 of 138 cases of secondary and tertiary spread occurred among health care workers. In Toronto, 73 of 144 such cases involved health care workers.2 (So far in the United States, hospital outbreaks have not occurred and two of 66 probable cases involve a health care worker.)3

In light of these hospital-based outbreaks, Bill Borwegen, MPH, occupational safety and health director for the Service Employees International Union (SEIU) in Washington, DC, called for research on the effectiveness of N-95s against the SARS virus.

"Where is the documentation that the N-95s are adequate?" says Borwegen. "All we know is that we have 15 victims in Canada" who were infected despite wearing protective equipment.

In hospitals with a large number of SARS patients, nurses have been wearing the N-95 respirators for virtually their entire shift. That may make it more difficult to continuously maintain infection control standards, employee health experts say.

Aerosol-generating procedures, such as intubation, appear to be particularly risky. In one Toronto case, nine health care workers caring for a SARS patient while he was intubated developed suspected or probable SARS.

For hospital employee health, the specter of SARS adds a new imperative. Some facilities already are equipping additional employees with respirators to ensure protection against SARS, including security, housekeeping, and registration staff. For example, at Marshfield (WI) Clinic, about 300 employees are fit-tested for respirators to work with tuberculosis patients. About 1,000 more may need respirators to protect against a SARS patient who could walk into an outpatient center, says Bruce Cunha, RN, MS, manager of employee health and safety.

"It takes about 15 minutes to do a fit test, if you’re zipping right through them," he says. "[For] 1,000 people, [fit-testing] eight hours a day, it would take six weeks. If I’ve got to go back now and refit [the other employees], I’ve got another issue. I don’t have even my basic core group."

If the fit tests occurred every year, Cunha says he would need to hire another employee to conduct them. "It’s not feasible, and it really doesn’t make any sense to have different protocols for different diseases," he says.

Hogan notes that OSHA does not have the legal authority to include SARS in the tuberculosis respiratory standard (1910.139), which was created as an interim measure while the agency was developing a tuberculosis standard.

Meanwhile, Cunha has purchased 12 additional PAPRs, which can be used by different employees after disinfecting.

Just how important is fit-testing of N-95s? That question is coming under scrutiny as the CDC investigates hospital-based outbreaks in Canada. Several health care workers developed SARS despite the use of protective equipment, including N-95 respirators and face shields. Canada did not require respirator fit-testing. In one reported case, nine health care workers caring for a SARS-infected physician at the time he was intubated subsequently developed SARS symptoms. The primary nurse has a small beard and reported feeling air move around his N-95 mask.1

Although SARS cases began to diminish in May, hospitals remained at high alert for potential cases. "It only takes one patient in an infectious state to slip through the cracks," noted Gerberding.

CDC is recommending a 10-day quarantine for health care workers who have unprotected "high-risk" exposure to SARS patients. "Unprotected high-risk exposure is defined as presence in the same room as a probable SARS patient during a high-risk aerosol-generating procedure or event and where recommended infection control precautions are either absent or breached," the CDC said. (See CDC’s algorithm.)

High-risk procedures include aerosolized medication treatments, diagnostic sputum induction, bronchoscopy, endotracheal intubation, airway suctioning, and close facial contact during a coughing paroxysm, the CDC said.

Other health care workers with unprotected exposures should take their temperature twice a day and report to employee health each day for 10 days to check for early symptoms, the CDC advises.

Hospital workers are particularly vulnerable to "superspreaders" — patients who are highly infectious. "The transmission efficiency may vary widely from individual to individual," said John Jernigan, MD, MS, leader of clinical and infection control in CDC’s SARS investigation team, in a webcast. In one cluster of cases in Singapore, five patients were associated with transmission to large numbers of people, while 81% of those infected subsequently infected did not transmit the virus.

"We don’t understand this phenomenon and what makes a person more likely to be involved with large numbers of secondary transmissions," Jernigan says.

So far, the United States has not encountered a superspreader. But Gerberding cautions, "If we were unfortunate enough to have someone with unrecognized SARS be admitted to a hospital or be present in an environment where they could expose many other people, we too could have a cascade of transmission established."

At this point, there are no distinguishing features of a superspreader. "We can’t tell, up front, who’s going to be infectious and who isn’t," she says.

Surface contamination may be another route of infection of health care workers. In the Canadian transmission, health care workers could have infected themselves when they removed their personal protective equipment, CDC reported.

"Many health care workers apparently lacked a clear understanding of how best to remove PPE without contaminating themselves," investigators reported.

The proper order, according to the report, is the removal of gloves first, followed by the mask and goggles. Hand hygiene then should be performed with hand washing or alcohol-based hand rubs.


1. Lee ML, Chen CJ, Su IJ, et al. Severe acute respiratory syndrome — 2003. MMWR 2003; 52:461-466.

2. Ofner M, Lem M, Sarwal S, et al. Cluster of severe acute respiratory syndrome cases among protected health care workers —- Toronto, Canada, April 2003. MMWR 2003; 52:433-436.

3. Centers for Disease Control and Prevention. Update: Severe acute respiratory syndrome — May 28, 2003. MMWR 2003; 52:500-501.