Download Febrile respiratory illness in the intensive care unit setting

Febrile respiratory illness in the intensive care unit setting:
an infection control perspective
Matthew P. Mullera and Allison McGeerb
Purpose of review
We have examined studies published since the severe
acute respiratory syndrome outbreak that elucidate the
mode of transmission of respiratory pathogens and the
optimal means of interrupting their transmission, focusing
on transmission in the intensive care unit.
Recent findings
The severe acute respiratory syndrome may be transmitted
by the droplet, contact and occasionally the airborne route.
Transmission occurred most frequently when healthcare
workers failed to use standard precautions such as hand
washing or personal protective equipment designed to limit
droplet and contact transmission. Aerosol-generating
procedures increased transmission, but incomplete use of
personal protective equipment during procedures was
common. Recent publications have stressed the benefits of
appropriate staffing levels, the use of single occupancy
rooms, the immunization of healthcare workers against
influenza, and the importance of healthcare workers
remaining home when ill in reducing the morbidity and
mortality of respiratory infection within the intensive care
unit.
Summary
Most respiratory pathogens can be transmitted by more
than one route. Despite this, healthcare worker awareness
of clinical syndromes associated with respiratory pathogens
that require airborne precautions, combined with the use of
standard precautions for all patients, and contact/droplet
precautions for patients with undifferentiated febrile
respiratory illness should be effective in interrupting the
transmission of respiratory pathogens within the intensive
care unit.
Keywords
infection prevention and control, intensive care unit,
respiratory tract infection, severe acute respiratory
syndrome
Curr Opin Crit Care 12:37–42. ß 2006 Lippincott Williams & Wilkins.
a
Department of Internal Medicine, Infectious Diseases Division, University of
Toronto, Mount Sinai Hospital, Toronto, Ontario, Canada M5G 1X5 and
b
Department of Microbiology, University of Toronto, Mount Sinai Hospital, Toronto,
Ontario, Canada M5G 1X5
Correspondence to Matthew P. Muller, MD, FRCPC, Department of Internal
Medicine, Infectious Diseases Division, University of Toronto, Mount Sinai Hospital,
Toronto, Ontario, Canada M5G 1X5
Tel: +1 416 586 3118; fax: +1 416 586 3140; e-mail: [email protected]
Current Opinion in Critical Care 2006, 12:37–42
Abbreviations
HCW
ICU
PAPR
PPE
SARS
VAP
healthcare worker
intensive care unit
powered air-purifying respirator
personal protective equipment
severe acute respiratory syndrome
ventilator-associated pneumonia
ß 2006 Lippincott Williams & Wilkins
1070-5295
Introduction
Febrile respiratory illness is the most common reason for
admission to an intensive care unit (ICU) [1]. In many
cases, the illness is caused by infection and the infecting
pathogen is transmissible. Infection control strategies
designed to interrupt the transmission of respiratory
pathogens in the ICU setting were tested during the
global outbreak of the severe acute respiratory syndrome
(SARS), generating new insights into the mode of transmission of respiratory pathogens and the optimal strategies to interrupt transmission.
Although the general principles of infection control are
no different in the ICU than in other areas of the hospital,
patients with respiratory infection requiring ICU admission provide a number of specific challenges. Such
patients are at the severest end of the clinical spectrum.
For some infections, such as SARS, patients may be more
infectious at the time of their ICU admission than at any
other time during their illness [2,3]. ICU patients
frequently require potentially aerosol-generating procedures, such as endotracheal intubation, tracheal suction,
nebulized medications and bronchoscopy. The transmission of SARS was notably associated with healthcare
worker (HCW) involvement in such high-risk procedures
[3,4,5,6].
We have examined the recent literature on infection
control strategies designed to prevent the transmission
of respiratory pathogens in the ICU. Much of this literature focuses on SARS, but still provides important lessons
that can be applied to other pathogens. We will not
provide a general review of infection control within the
ICU or address the prevention of ventilator-associated
pneumonia (VAP). Instead, this review focuses on the
exogenous transmission of respiratory pathogens within
the ICU. VAP results primarily from endogenous infection, although infection control strategies are critical
37
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
38 Respiratory system
in preventing VAP and in reducing VAP caused by
antibiotic-resistant organisms [7,8].
Rationale for concern about the transmission
of respiratory pathogens
The majority of patients with febrile respiratory illness
admitted to the ICU do not pose a direct risk to HCWs
either because the pathogen is not easily transmitted
from person to person or because the resultant illness
is unlikely to be severe in a healthy individual. Interrupting transmission remains a priority, however, as
uncommon but virulent pathogens such as Mycobacterium
tuberculosis or invasive group A streptococcus are capable
of causing severe illness even in healthy HCWs. Furthermore, viral respiratory pathogens spread rapidly, increase
mortality and morbidity in vulnerable ICU patients, and
can cause illness among HCWs resulting in significant
work shortages.
Unfortunately, the etiology of respiratory infection is
usually unknown at the time of ICU admission [9].
Therefore, a standard approach is required to protect
both ICU HCWs and patients from the most common
and dangerous respiratory pathogens.
Transmission of respiratory pathogens
Understanding the transmission of respiratory pathogens
is the key step in developing a rational strategy to prevent
infection. Fortunately, although there are many respiratory pathogens, there are only three routes of transmission within the ICU: airborne, droplet, or contact
transmission (Table 1). Most respiratory pathogens are
believed to be transmitted primarily or exclusively by the
droplet route. Airborne transmission is considered to
occur only with a select group of organisms: M. tuberculosis, measles, smallpox, and varicella-zoster virus (e.g.
chicken pox or disseminated zoster). Contact transmission is recognized as a potential cause of transmission
for many pathogens, but is generally considered less
significant than droplet spread.
Accumulating evidence suggests that the distinction
between droplet and airborne transmission may not be
as clear-cut as previously thought, and that the role of
contact transmission may have been underestimated.
SARS provides an example of the complexity of respiratory virus transmission. Initial reports suggested that
SARS was transmitted by the droplet route [10,11].
However, in the Amoy Gardens outbreak, SARS cases
appeared rapidly in several different apartment buildings
in a manner atypical of contact or droplet transmission
[12]. The airflow dynamics within and around the
buildings corresponded to the distribution of illness,
suggesting airborne transmission. The current hypothesis
is that a bathroom exhaust fan aerosolized contaminated
feces into an airshaft, with subsequent airborne transmission [12]. Reports in which HCWs developed SARS
despite the appropriate use of personal protective equipment (PPE) effective for droplet transmission and
instances of transmission over distances greater than
1 m are also suggestive of airborne transmission
[5,13,14]. Aerosol-generating procedures may generate
finer droplets than those produced spontaneously by
coughing, resulting in transmission beyond 1 m and in
‘extended droplet’ transmission [15]. Others have
suggested that the strict definition of airborne transmission should be modified to include obligate (i.e. only
transmitted by the airborne route), preferential (i.e. most
commonly transmitted by the airborne route), or opportunistic (i.e. transmitted by the airborne route under
specific circumstances) airborne transmission [15,16].
Influenza is another example of a virus considered to be
transmitted primarily by the droplet route. Both animal
models and observational studies of human outbreaks,
however, suggest that airborne transmission can occur
with influenza [17–21]. In one outbreak a single ill
passenger on an airplane with an inactivated ventilation
system transmitted influenza to 91% of the passengers
and crew, a finding highly suggestive of airborne transmission [17].
Contact transmission is important for a number of viral
respiratory tract infections, including respiratory syncytial virus, parainfluenza virus and adenovirus [8]. Hand
washing or hand disinfection has been associated with
a reduction in the incidence of viral respiratory tract
infections in several contexts [22,23,24]. Although
droplet transmission was considered the primary mode
of transmission for SARS, hand hygiene was consistently
Table 1 Routes of transmission of respiratory pathogens in the intensive care unit
Route
Description
Airborne
Small droplets (< 5 mm) expelled from the respiratory tract of an infected individual dry and shrink while airborne,
forming droplet nuclei capable of remaining airborne for prolonged periods and traveling large distances before being
inhaled into the distal airways of a susceptible individual
Large (> 10 mm) droplets are expelled from the respiratory tract of an infected individual and come into contact with the oral,
nasal or conjunctival mucosa of a susceptible individual. The large size of the droplet ensures that they fall rapidly and prevents
transmission over distances > 1 m
Results from physical contact with an infected or colonized individual or through physical contact with a contaminated object
Droplet
Contact
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Febrile respiratory illness in the intensive care unit Muller and McGeer 39
identified as an effective means of reducing SARS transmission [8,25,26,27]. Direct contact with respiratory
secretions was also an independent predictor of SARS
risk, providing further evidence of the importance of
contact transmission in SARS [26].
Given the uncertainty about the routes of transmission for
many respiratory pathogens, including SARS and influenza, infection control strategies designed to reduce the
transmission of infection from patients with undifferentiated febrile respiratory illness should not be strictly
focused on the prevention of droplet transmission. For
most patients with febrile respiratory illness, it should be
assumed that droplet or contact transmission may occur,
and that airborne transmission may also be important
when there is a risk of aerosolization. This cautious
approach is particularly important for virulent organisms
such as the SARS coronavirus or pandemic influenza
[28 –30].
Strategies to interrupt the transmission of
respiratory pathogens
The transmission of respiratory pathogens can be interrupted by limiting the number of susceptible or infected
individuals in the ICU or by protecting the susceptible
from the infected individuals.
Removing susceptible and infected individuals from the
intensive care unit
Susceptible individuals can be ‘removed’ from the ICU
by changing their immunological status from susceptible
to immune through immunization. Although immunization is not available for most respiratory pathogens,
influenza is an important exception. It has been repeatedly demonstrated that yearly influenza vaccination of
HCWs in long-term care hospitals reduces all-cause
mortality among the patients in their care by 30–40%
[31,32]. Vaccination of ICU staff would be expected to
confer similar benefits, particularly for elderly or immunocompromised patients, and would reduce illness and
time off work among HCWs.
Although infected patients cannot easily be removed
from the ICU, infected HCWs can and should be. HCWs
with symptoms of acute respiratory tract infection (e.g.
fever and cough) should not report to work or be involved
in the care of ICU patients, as this puts patients at risk of
severe complications and will result in illness among
other HCWs [8,33].
Finally, although infected patients cannot be completely
removed from the ICU, caring for such patients in a single
room limits the potential exposure of other patients and
staff. The SARS outbreak also demonstrated the importance of having negative pressure, single-occupancy
ICU rooms available. Two recent reports advocated that
future ICUs consist exclusively of single-occupancy
rooms, largely as a result of the recognition that single
rooms are associated with a reduced risk of transmission
of infectious pathogens and provide maximum flexibility
during outbreaks of potentially airborne pathogens
[34,35–38].
Interrupting transmission from infected to susceptible
individuals within the intensive care unit
Guidelines have described the infection control precautions that should be used for all patient contacts (e.g.
routine practices or standard precautions) and for patient
contacts when specific infectious pathogens are suspected (e.g. additional precautions) [39,40]. Routine
practices/standard precautions include hand washing or
hand disinfection before and after all patient contacts and
the use of appropriate PPE when there is the potential for
contact with blood or bodily fluids [39,40]. PPE may
include the use of gloves, gowns, surgical masks and
eye protection. For example, routine venipuncture
requires the use of gloves. When performing endotracheal intubation or a nasopharyngeal swab that may
induce coughing or sneezing, the use of gloves, gowns,
masks and eye protection is required. Additional precautions require that HCWs are aware of the clinical syndromes associated with organisms that require additional
precautions (e.g. fever, cough and an upper lobe infiltrate
are suggestive of tuberculosis and require airborne precautions) [39].
Studies of SARS transmission among HCWs implicated
failures in the appropriate use of PPE as a cause of
transmission [3,4,25,41,42]. These were not only
failures of SARS-specific (i.e. additional) precautions,
but also failures of routine practices and standard precautions, such as the failure to perform hand hygiene,
lack of eye protection during procedures likely to cause
splashes, or the failure to wear gloves for contact with
mucous membranes and respiratory secretions [4]. In
some cases, failures may have resulted from a lack of
appropriate infection control training or a lack of access to
appropriate equipment [41].
The failure of HCWs to use accepted infection control
precautions is a commonly described phenomenon.
Studies consistently show that HCW compliance with
hand hygiene recommendations is less than 50%, and
that compliance is lowest when it is most important: in
the ICU, for invasive procedures and for emergency
procedures [43–45]. Studies of adherence to airborne
precautions during the care of patients with drugresistant tuberculosis have also shown an inconsistent
use of precautions [46].
Although studies of SARS have suggested that inadequate education and understanding of the need for and
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
40 Respiratory system
application of PPE is one reason for reduced adherence to
hand hygiene and the use of PPE, poor compliance,
particularly in the ICU, has also been correlated with
increased workload [43,47]. Recent studies have also
demonstrated that a low nurse-to-patient ratio is associated with an increased risk of bloodstream infection in
patients, presumably because of a breakdown in appropriate infection prevention practice [48–50].
The bottom line is that current infection prevention
recommendations, if applied consistently and correctly,
are capable of preventing virtually all transmission of
respiratory pathogens in the ICU. Improving adherence
among HCWs is the biggest challenge, and a multifaceted approach is required. Important measures include the provision of clear infection control guidelines,
infection control education, feedback on rates of
adherence and infection, adequate and accessible supplies, adequate staffing levels, positive role models
among HCW leadership, a positive safety climate, and
administrative support for infection control [43,51,52].
Controversies over the selection and use of
personal protective equipment
Although obtaining adequate adherence to existing
guidelines is probably more important than improving
or revising these guidelines, it is obvious that such
guidelines should be based on the best evidence available. The simplest and most effective measures should
be recommended. Several areas of controversy in the
appropriate selection and use of PPE for ICU patients
with febrile respiratory illness will now be discussed.
N95 versus surgical masks
During the SARS outbreak, N95 masks were recommended for HCWs caring for SARS patients. Several
studies suggested that both surgical and N95 masks were
protective, although in one of the studies cases related to
an index patient receiving nebulized therapy were
excluded from the analysis [25,42]. The authors concluded that droplet and contact precautions were sufficient provided that ‘no aerosolizations are expected’ [25].
In a Vietnamese outbreak in which N95 masks were
not available for 3 weeks, no transmission occurred,
suggesting that surgical masks are sufficient to protect
from SARS [53]. A fourth study confirmed that both N95
and surgical masks confer protection but found a 50%
reduction in risk with N95 compared with surgical masks
[42]. This finding was not statistically significant,
however.
Taken together, these results suggest that in most cases
combined droplet/contact precautions that include the
use of a surgical mask are sufficient to prevent SARS
transmission. Limited data suggest that the use of an N95
mask may confer additional protection. The use of an
N95 mask may be particularly important when HCWs are
involved in potential aerosol-generating procedures,
although this was not directly addressed in these studies.
Current Canadian guidelines no longer recommend N95
masks for the routine care of patients with undifferentiated febrile respiratory illness, but it may still be
reasonable to consider the use of an N95 mask in combination with droplet/contact precautions if there is a
suspicion that a highly virulent and transmissible
pathogen may be present (e.g. avian influenza, SARS)
[28,33].
Fit testing
PPE must be used properly to be optimally effective. Fit
testing involves testing HCWs to determine whether
they can taste or smell chemical agents released while
they wear the N95 mask. Fit checking is the process of
ensuring that a seal has been obtained after putting on the
mask. Fit checking should be performed every time an
N95 mask is used.
HCWs who have not been trained in the use of the N95
mask frequently fail fit testing [46,54]. Mandatory fit
testing provides an opportunity to educate HCWs on the
correct use of the N95 and the importance of fit checking,
and also allows formal testing of the mask’s fit. Volunteers
who do not receive fit testing have higher mucosal
exposure to droplets than those who have fit testing
[15,55]. When education was compared with education
and fit testing, there was no difference in the proportion
of HCWs who could subsequently pass a fit test [56]. The
selection of good quality masks by the institution, and the
provision of sufficient education to permit HCWs to
select the best fitting mask and perform a fit check each
time they use it, is probably more important than fit
testing in ensuring that HCWs are using N95 masks
correctly [15,56].
Powered air-purifying respirators
During the SARS outbreak, an apparent failure of PPE
led to recommendations for the use of powered airpurifying respirators (PAPRs) during aerosol-generating
procedures [6]. PAPRs have been recommended for use
when caring for patients with active tuberculosis, but
these recommendations were challenged because of concerns about cost, the psychological impact on patients,
and reduced vision, hearing, and ability to communicate
[57]. The use of PAPRs was more acceptable to HCWs
for SARS than it had been for tuberculosis, presumably
because of a higher perceived risk [58].
No evidence is available on the effectiveness of PAPRs
compared with the use of N95 masks, eye protection,
gowns and gloves. Although the performance of aerosolgenerating procedures was associated with SARS transmission in several studies, failure to use the appropriate
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Febrile respiratory illness in the intensive care unit Muller and McGeer 41
PPE or to use PPE correctly were frequently described
and may have been the primary cause of infection
[3,4,5,6]. In two studies that adjusted for incorrect
or incomplete PPE use [41,59], participation in a
high-risk procedure was not associated with SARS
transmission. In addition, concern has been raised that
difficulties in the removal of PAPRs without selfcontamination may actually put HCWs at risk [59].
Clearly, if PAPRs are to be used, HCWs should be
carefully trained in their use, removal and maintenance.
There is currently no evidence to suggest that PAPRs
should be used for ICU patients with undifferentiated
febrile respiratory illness, either for routine care or during
aerosol-generating procedures. The value of PAPRs
during the care of ICU patients known to have SARS
or other highly virulent organisms remains uncertain. It
is important to recognize that any benefits of PAPRs
accrue to HCWs, whereas their disadvantages pose risks
primarily for patients, a situation that complicates the
assessment of their use.
Conclusion
Patients with undifferentiated febrile respiratory illness,
when admitted to the ICU, are a potential risk to both
HCWs and other patients. Although the nature of infectious disease transmission is complex, a recognition of
syndromes associated with airborne pathogens, and the
consistent use of hand hygiene and droplet/contact
precautions for patients with febrile respiratory illness,
will be sufficient to interrupt transmission in the vast
majority of cases. The biggest current challenge lies in
identifying and implementing effective strategies
designed to improve HCW adherence to these basic
infection control priniciples.
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