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Cluster of Severe Acute
Respiratory Syndrome Cases Among Protected
Health-Care Workers
Toronto, Canada, April 2003
Infections
among health-care workers (HCWs) have been a common
feature of severe acute respiratory syndrome (SARS) since its emergence. The
majority of these infections have occurred in locations where
infection-control precautions either had not been instituted or had been
instituted but were not followed. Recommended infection-control precautions
include the use of negative-pressure isolation rooms where available; N95 or
higher level of respiratory protection; gloves, gowns, and eye protection;
and careful hand hygiene. This report summarizes a cluster of SARS cases
among HCWs in a hospital that occurred despite
apparent compliance with recommended infection-control precautions (1).
The
index patient was a Canadian family physician aged 54 years with a history of
hyperlipidemia, hypertension, and noninsulin-dependent diabetes controlled on oral
medications. During April 1--2, 2003, he examined three patients who were
family members involved in a community cluster of SARS in Toronto, Ontario (2). No infection-control
precautions were used. On April 4, he had fever, myalgia,
headache, mild diarrhea, and a dry cough; on
medical evaluation, he had a clear chest radiograph, but he continued to feel
ill during home isolation. On April 8, he was reevaluated
and found to have a left upper-lobe infiltrate on a repeat chest radiograph;
he was admitted to the SARS ward of hospital A. During the next several days,
he remained febrile with increasing cough, although his diarrhea
resolved. On April 12, the patient's temperature was 104.7º F
(40.4º C), his chest radiograph showed worsening pneumonia, and he
required supplemental oxygen for hypoxia. He was treated with ipratropium bromide and albuterol
sulfate by metered dose inhaler, intravenous (IV) ribavirin, and steroids. On April 12, he had a nearly
constant cough and was assessed for transfer to the intensive care unit
(ICU). On April 13, the patient was transported to the ICU in a wheelchair on
100% oxygen through nonrebreather face mask. Soon
after his arrival in the ICU, his measured oxygen saturation decreased to
60%, and he was placed on positive pressure ventilation through face mask (BiPAP). Because of severe cough and agitation, he removed
the mask repeatedly despite administration of IV sedation. After an
approximately 2-hour attempt to provide oxygen through BiPAP,
the patient was intubated. During intubation, he had copious frothy secretions that later
obstructed the ventilator tubing, requiring disconnection and drainage. Once
supported with mechanical ventilation, the patient was sedated further by
using IV midazolam/morphine sulfate.
Later
that evening, the patient was switched from assist-control ventilation to
high-frequency oscillatory ventilation (HFOV) because of continued inadequate
oxygenation. At this point, the patient's condition stabilized, and he was
maintained on HFOV for 7 days, after which he was switched back to
assist-control mode. As of May 14, the patient remained in critical condition.
Both a sputum sample collected from the patient on April 13 and a stool
sample collected on May 5 were positive for the SARS-associated coronavirus (SARS-CoV) by
polymerase chain reaction.
During
April 15--21, nine HCWs who had cared for this patient
around the time he was intubated had illnesses
consistent with the World Health Organization case definition for suspect or
probable SARS (3); another two HCWs had
symptoms that were not consisent with the case
definition (Table). Six of these 11 HCWs had been
present during the intubation procedure. Interviews
with affected HCWs indicated that they all had worn
the recommended personal protective equipment each time they entered the
patient's room, including gown, gloves, PCM2000™ duckbill masks
(Kimberly Clark Health Care, Roswell, Georgia), and goggles with or without
an overlying face shield.
The
room in which the intubation took place was at
negative pressure to the hallway, and all air was vented to the outside after
high-efficiency particulate air filtration; however, no anteroom was
available, and removal of personal protective equipment took place in a
staged manner both inside and outside the room, with the door kept closed
between each entry and exit. Understanding of the correct order to remove
personal protective equipment (PPE) (i.e., gloves first followed by mask and
goggles) varied among HCWs.
Masks
worn by HCWs inside ICU rooms and halls were
changed on leaving each patient's room; however, no formal respiratory
protection program existed at the hospital, and individual workers had not
been fit tested. In addition, the primary nurse for the patient had a small
beard and reported that his mask did not fit well. Although he wore both a
PCM2000™ duckbill mask and a surgical mask with face shield, he
sometimes could feel air entering around the sides of his mask.
Reported by: M Ofner,
Div of Blood Safety, Nosocomial and Occupational
Infections; M Lem, S Sarwal, Field Epidemiology Training
Program, Health Canada; M Vearncombe,
A Simor, Sunnybrook and Women's College Health
Sciences Centre, Toronto, Ontario, Canada. SARS Investigative Team, CDC.
Editorial Note:
Transmission
of SARS appears to result primarily from direct patient contact or contact
with large respiratory droplets in the close vicinity of an infected person. Despite
apparent limited modes of transmission, SARS has been known to spread
extensively among HCWs in various settings. For
example, among 138 cases of secondary and tertiary spread in Hong Kong, 85 (62%) occurred among HCWs (4); among 144 cases in Toronto, 73 (51%) were HCWs (5). SARS infection of HCWs
might be related to increased contact with respiratory secretions, contact
with patients during a more contagious phase of critical illness, contact
with particular patients at increased likelihood of spreading SARS (i.e.,
super spreaders), or exposure to aerosol-generating patient-care procedures (6).
Health
Canada and CDC are aware of several unpublished
reports of SARS clusters among unprotected HCWs
involved with intubation, both in Canada and outside North America. The cluster described in this
report might be unique, as HCWs appear to have
followed infection-control precautions recommended by Health Canada. The Health Canada
recommendations, although similar to those of CDC, differ from CDC guidelines
with respect to respiratory protection. CDC guidelines specify use of
respirators approved by the National Institute for Occupational Safety and
Health (NIOSH) rated at an N95 level of protection or greater (7). Health
Canada recommends use of "N95 equivalent"
respirators (8). The respirators used in hospital A, although
compliant with Canadian public health recommendations, were not
NIOSH-approved. In addition, at the time these exposures occurred, fit
testing was not recommended by Canadian public health authorities; such
testing has been mandated in the United States since 1972.
Endotracheal intubation might
cause an awake or a semiconcious patient to cough
and often necessitates open suctioning of respiratory secretions. In
addition, other potentially aerosol-generating procedures were performed on
this patient, including BiPAP, during which air
might be forced out around the face mask and thereby aerosolize secretions,
and HFOV, during which exhaust from the ventilator tubing is more likely to
escape without passing through an antibacterial/antiviral filter. The patient
also was in his second week of illness with clinical deterioration and severe
cough, possibly explaining why HCWs who were exposed
to the patient only before his transfer to the ICU became infected, as the
viral loads of patients at this stage of illness appear high (9).
Direct
contact with the patient or contact with an environment contaminated by large
respiratory droplets might have led to HCWs
infecting themselves as they removed their PPE. For example, HCWs have been known to spread other nosocomial
pathogens from patient to patient despite the use of barrier precautions;
even in the best of circumstances, correct use of PPE might be suboptimal. If
contact or droplet spread alone were responsible for this cluster, a lapse in
technique would be required on the part of each infected HCW. Many HCWs apparently lacked a clear understanding of how best
to remove PPE without contaminating themselves. Alternatively, aerosolizing
procedures or the patient's own cough might have led to airborne spread, and
either the level of respiratory protection used or the manner in which it was
used did not prevent transmission.
This
cluster is part of a larger number of cases in HCWs
in hospitals in the greater Toronto area who have become infected while
caring for SARS patients since directives for contact, droplet, and airborne
precautions were instituted at the provincial level on March 28 (1). Further
investigation is necessary to determine factors associated with transmission
despite the apparent use of recommended infection-control precautions.
HCWs caring for SARS patients should be properly
trained in the correct use and removal of PPE and reminded of the importance
of hand hygiene. Patients who are experiencing rapid clinical progression
with severe cough during their second week of illness should be considered
particularly infectious. Procedures that might generate aerosols (e.g., nebulized medications, BiPAP,
or HFOV) should be avoided if possible. When intubation
is necessary, measures should be taken to reduce unnecessary exposure to HCWs, including reducing the number of HCWs present and adequately sedating or paralyzing the
patient to reduce cough. Updated interim infection control precautions for
aerosol-generating procedures on patients who have SARS are under development
and will be available from CDC at http://www.cdc.gov/ncidod/sars/ic.htm.
References
- Health Canada. SARS among Ontario health care workers---SARS
epidemiologic summaries: April 26, 2003. Available at http://www.hc-sc.gc.ca/pphb-dgspsp/sars-sras/pef-dep/sars-es20030426_e.html.
- Health Canada. Epi-Update:
Interim report on the SARS outbreak in the Greater Toronto Area, Ontario, Canada, April
24, 2003. Available at http://www.hc-sc.gc.ca/pphb-dgspsp/sars-sras/pef-dep/gta-20030424_e.html.
- World Health Organization. Case
definitions for surveillance of Severe Acute Respiratory Syndrome
(SARS). Available at http://www.who.int/csr/sars/casedefinition/en.
- Lee N, Hui D, Wu A, et al. A major outbreak of severe
acute respiratory syndrome in Hong Kong. N Engl
J Med 2003. Available at http://content.nejm.org/cgi/reprint/NEJMoa030685v2.pdf.
- Booth CM, Matukas
LM, Tomlinson GA, et al. Clinical features and short-term outcomes of 144
patients with SARS in the Greater Toronto Area. JAMA 2003. Available at http://jama.ama-assn.org/cgi/reprint/289.21.JOC30885v1.pdf.
- Seto WH, Tsang D,Yung RW, et al., and
Advisors of Expert SARS Group of Hospital Authority. Effectiveness of
precautions against droplets and contact in prevention of nosocomial transmission of severe acute respiratory
syndrome (SARS). Lancet 2003;361:1519--20.
- CDC. Interim domestic guidance on the use
of respirators to prevent transmission of SARS, May 6, 2003. Available at http://www.cdc.gov/ncidod/sars/respirators.htm.
- Health Canada. Infection control guidance
for respirators (masks) worn by health care workers-frequently asked
questions, revised April 17, 2003. Available at http://www.hc-sc.gc.ca/pphb-dgspsp/sars-sras/ic-ci/sars-respmasks_e.html.
- Peiris JS, Chu
CM, Cheng VC, et al., and members of the HKU/UCH SARS Study Group. Clinical
progression and viral load in a community outbreak of coronavirus-associated SARS pneumonia: a prospective
study. Lancet 2003. Available
at http://image.thelancet.com/extras/03art4432web.pdf.
Table
![Table 1](../../../www.cdc.gov/mmwr/preview/mmwrhtml/figures/m219a1t.gif)
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