Crowding and Unsanitary Conditions Fostered SARS 'Super-Spreading'

HONG KONG, March 16 -- Crowded hospital units were a key factor that led to "super-spreading" outbreaks of severe acute respiratory syndrome (SARS) in China, according to researchers here.

Other key factors were a lack of washing and changing facilities for staffers and health-care workers who stayed on the job although they had respiratory symptoms, found Joseph Sung, M.D., Ph.D., of the Chinese University of Hong Kong.

The SARS epidemic of 2003 mainly affected two regions in China -- Guangzhou and Hong Kong -- with 1,567 and 1,755 probable cases, respectively, although smaller outbreaks occurred elsewhere around the world, Dr. Sung and colleagues noted online in the April 15 issue of Clinical Infectious Diseases.

Much of the disease was nosocomial, Dr. Sung and colleagues noted, but some hospital wards were the center of "super-spreading" events in which either:

• Three or more new cases were identified within eight to 10 days of the admission of an index SARS patient.
• A cluster of three or more cases was identified within eight days in a unit in which there was no known source of SARS.

One estimate suggested that more than 70% of all infections in Hong Kong and Singapore resulted from super-spreading events, the researchers noted.

To identify the factors involved, Dr. Sung and colleagues conducted a case-control study of 86 units in 21 hospitals in Guangzhou and 38 units in five hospitals in Hong Kong.

Case units were those in which super-spreading occurred, while control units were those that had SARS patients but did not experience super-spreading.

In a multiple-logistic regression model, six risk factors were significant:

• A distance between beds of a meter or less increased the risk by a factor of nearly seven. The odds ratio was 6.94, with a 95% confidence interval from 1.68 to 28.75, which was significant at P=0.008.
• Resuscitation performed in the ward increased the risk nearly four-fold. The odds ratio was 3.81, with a 95% confidence interval from 1.04 to 13.87, which was significant at P=0.04.
• Staff members who worked with symptoms increased the risk by a factor of 10. The odds ratio was 10.55, with a 95% confidence interval from 2.28 to 48.87, which was significant at P=0.003.
• If the index patient or the first patient with SARS admitted to a ward required oxygen therapy, the risk increased by a factor of four. The odds ratio was 4.30, with a 95% confidence interval from 1.00 to 18.43, which was significant at P=0.05.
• If the index patient or the first patient with SARS admitted to a unit required bilevel positive airway pressure ventilation, the risk increased 11-fold. The odds ratio was 11.82, with a 95% confidence interval from 1.97 to 70.80, which was significant at P=0.007.
• The availability of washing or changing facilities for staff decreased the risk by nearly 90%. The odds ratio was 0.12, with a 95% confidence interval from 0.02 to 0.97, which was significant at P=0.05.

"The lesson we learned during the SARS epidemic was that the hospital can be a breeding ground for infectious disease," Dr. Sung said. It is important, he added, to provide adequate space in hospital units and implement effective infection control measures."

He added that it's common for hospitals to put more patients in a unit during an epidemic, not fewer, but the findings show the danger of that practice.

The authors noted the lessons learned. They wrote, "With the current threat of avian influenza and other respiratory infections, such as tuberculosis, hospital wards have to be redesigned and managed in a manner to ensure that environmental factors associated with nosocomial infections are kept to the minimum."

"The importance of adequate spacing between beds and provision of washing or changing facilities for staffers cannot be overemphasized. Staffers with symptoms of respiratory infections should refrain from continuing their clinical duties. Adequate complementary protective devices at the source of infection (namely, infected patients) would have to be designed.

"Additional work needs to be conducted with regard to the safe use of oxygen therapy and/or ventilatory support among patients with respiratory infections."

The researchers said the study's strengths include a high rate of participation of the hospitals in the two regions, but added it is not clear how far the findings can be extended to the SARS outbreaks in other countries.