Download The Role of the Microbiology Laboratory in Surveillance and Control

The Role of the Microbiology Laboratory in Surveillance
and Control of Nosocomial Infections
ROBERT A. WEINSTEIN, M.D., AND GEORGE F. MALLISON, M.P.H.
Weinstein, Robert A., and Mallison, George F.: The role of
the microbiology laboratory in surveillance and control of
nosocomial infections. Am J Clin Pathol 69: 130-136, 1978.
The microbiology laboratory's rapid and consistent identification of nosocomial pathogens is a keystone in the surveillance
and control of hospital-acquired infections. In addition, the
laboratory serves as a source of expert consultation for
clinicians and infection control personnel and as an "early
warning center" for infection problems. In making its contributions to infection control most effective, the laboratory
must recognize its capabilities and limitations, must insure
that the materials and methods it uses and the specimens
it processes meet high standards, must provide retrievable
records, and must have a good working knowledge of
microbiologic technics used to evaluate both endemic and
epidemic infections. Moreover, because laboratory workers
come into contact daily with potentially infectious specimens and isolates, the laboratory's contributions to infection control should also include the prevention and surveillance of laboratory-acquired infections. (Key words:
Clinical microbiology; Infection control; Nosocomial infections; Laboratory-acquired infections.)
U.S. Department of Health, Education and Welfare,
Public Health Service, Center for Disease Control,
Bureau of Epidemiology, Atlanta, Georgia
Major Contributions towards Surveillance
and Control
Laboratories generally contribute directly to the
surveillance and control of nosocomial infections in
five ways. First, the laboratory records are an important surveillance tool and data source. Because
more than 80% of infections subsequently judged
to be nosocomial may be cultured in hospitals
with active infection surveillance and control programs, 56 the data gathered by infection control
personnel during "laboratory rounds," together with
data gathered from "clinical rounds," form an important base for calculation of infection rates for
various pathogens, by site of infection and by hospital service. 15
SINCE THE EARLY 1950's, when widespread
hospital-acquired staphylococcal disease first focused
attention on the problem of nosocomial infections,
the hospital and laboratory burden created by
nosocomial pathogens has increased greatly.1-4-7'33'68 At
present in the United States, nosocomial infections
affect more than 1.5 million patients each year and
add more than one billion dollars to the cost of healthcare delivery. 56 Although hospital laboratory capacities
are often strained by the sheer number of routine
specimens to be processed, each hospital also looks to
its lab for support in activities related to prevention, surveillance, and control of hospital-acquired
infections. 1,32 In this paper, we present the major
contributions that we feel the microbiology laboratory
can and should make toward infection control, we
discuss specific activities that can assist the laboratory
in making its contributions most effective, and we suggest how laboratory-acquired infections may be prevented and controlled.
Second, the laboratory results are a potential
"early-warning system" for the emergence within a
hospital of highly infectious pathogens, multiplyresistant organisms, and clusters of unusual infections.
In hospitals where formal surveillance has not yet been
established, laboratory workers may in fact be the only
personnel to see ward-by-ward culture results and
thus be in a position to detect infection trends.
Third, the microbiology laboratory is often called
upon for expertise in microbiologic sampling of the
hospital environment. Since surveillance of patient
disease and upgrading of patient-care policies and
practices should be the primary focuses of infection
control programs, microbiology and infection control
personnel should be prepared to curtail routine
microbiologic sampling and testing sharply. 115,61
Fourth, during nosocomial epidemics laboratory
personnel may conduct culture surveys of patients,
hospital personnel, and the environment. Large
numbers of cultures may have to be obtained, processed, and evaluated over a short period. Data
gathered by microbiology personnel in such surveys
may be crucial in identifying the reservoir and
mode of spread of epidemic organisms.
Finally, a clinically oriented member of the labora-
Received April 12, 1976; received revised manuscript January
21, 1977; accepted for publication January 21, 1977.
Dr. Weinstein's present address is Department of Medicine,
University of Chicago Hospitals, Chicago, Illinois 60637.
Address reprint requests to Hospital Infections Branch, Bacterial
Diseases Division, Bureau of Epidemiology, Center for Disease
Control, Atlanta, Georgia 30333.
0002-9173-78-0200—0130$00.85 © Ame:rican Society of Clinical Pathologists
130
ROLE OF THE LABORATORY IN INFECTION CONTROL
Vol. 69 . No. 2
tory staff can contribute significantly by serving on
the infection control committee. 5,15,32,4 ° Input by this
member of the committee is essential in maintaining
a harmonious working relationship between clinical,
infection control, and microbiology personnel.
Specific Activities
Regular Assessment
and Handling
of Specimen
Collection
Improperly collected or transported specimens 28
may give inaccurate results even in the best clinical
laboratories, and are likely to result in improper clinical decisions by physicians, unnecessary labor by
laboratory personnel, excessive patient charges, and
misleading epidemiologic data. Certain laboratory
findings suggest specific handling errors. For example,
the frequent recovery of two or more different organisms or the frequent finding of 10 3 -10 4 organisms
per ml in clean-voided urine specimens strongly
suggests unsatisfactory technic in collecting specimens, a delay in transporting specimens to the
laboratory, or a delay in culturing the specimens after
receipt. 36 The frequent failure to culture organisms
from deep abscesses of patients who are not receiving
antibiotics, or the failure to isolate pathogens seen on
Gram-stained material from presumed anaerobic
infections, suggests the use of aerobic transport vials,
delay (or inappropriate refrigeration) of specimens in
transit, or the use of inadequate laboratory technics for isolating anaerobes. 217 The finding of negative acid-fast cultures from a high percentage of
specimens with positive acid-fast smears suggests
unsatisfactory sputum collection and handling, errors
in staining, or errors in culture technic. 6770
To help avoid such problems, it is important to
assess specimen collection and handling regularly.
An ongoing analysis of the frequency with which
probable contaminants are isolated from clinical
specimens provides an indirect measure of specimen
collection on the ward. Once these data have been
compiled, wards with the highest frequencies of polymicrobial urine specimens, for example, can be singled
out for evaluation and, when necessary, intensive inservice education by laboratory or infection control
personnel. Likewise, personnel who draw blood specimens that frequently contain diphtheroids, coagulasenegative staphylococci, or other probable skin contaminants may need to be reinstructed in aseptic
technic. Periodic review of the relative incidence of
false-positive acid-fast smears may highlight problems
in sputum collection and processing. 70
Microscopic preview of certain types of specimens
may help to avert culturing inadequately collected
131
material. For example, after a prospective study at
the Mayo Clinic showed that sputum specimens with
more than ten squamous epithelial cells per low-power
(xlOO) Gram-stained field were usually contaminated
with oropharyngeal secretions, all such specimens at
that institution have been rejected for bacteriologic
culture (and the staff submitting the specimen notified).42 Scoring systems for use in determining acceptable sputum, wound, vaginal, cervical, and other
specimens have also been described. 3 - 4
Periodically, matched specimens (one taken directly
to the laboratory and cultured immediately and the
other transported in the usual manner) should be
examined to determine whether a significant transport
delay exists. 31 Some hospitals also use laboratory
slips that require recording both the time the specimen
was collected and the time the laboratory received it,
so that transport time can be continuously monitored and the culturing of excessively old specimens
avoided.
With the increasing recognition of anaerobes as
potential nosocomial pathogens, laboratory personnel
need to be especially alert for errors in collection
or transport of anaerobic specimens. 217 - 22 ' 23 ' 41 Large
numbers of anaerobic organisms are present in the
normal flora of the skin, oral cavity, and gastrointestinal tract; thus, swabs from superficial portions
of skin or mucous membrane lesions, specimens of
expectorated sputum (or bronchoscope specimens),
and any materials contaminated with feces should be
considered inappropriate for anaerobic culture. Frequent submission of such specimens, or of specimens
such as urine that are rarely infected by anaerobes, 54
for anaerobic culture suggests the need for in-service
education of hospital personnel.
Accurate and Consistent Identification of Isolates
Recognition and evaluation of hospital-acquired
infections depends on accurate and consistent identification of microorganisms. Not infrequently, CDC
personnel investigate an apparent outbreak only to
find that the problem resulted from errors in or
changes in laboratory procedures. For example, an
"outbreak" of Staphylococcus aureus infections was
caused by delayed reading of coagulase tests, resulting
in the misidentification of coagulase-negative organisms as coagulase-positive. In another hospital,
improvements in laboratory technic that allowed
accurate identification of Herellea vaginicola organisms, for the first time in that institution, resulted in an apparent "outbreak of Herellea infections."
Of even greater concern, incomplete identification
or misidentification of organisms may obscure real
132
WEINSTEIN AND MALLISON
problems and make retrospective epidemiologic investigation impossible. For example, a report of'' Klebsiella-aerobacter group" is not only phrased in obsolete terminology but also fails to distinguish between Klebsiella and Enterobacter, organisms that are
characterized by different antimicrobial sensitivities
and may have different epidemiologic patterns within
the hospital. 63 Along the same lines, identifying an
isolate as Pseudomonas cepacia, an organism frequently associated with illness caused by contaminated
dilute aqueous benzalkonium chloride or similar antiseptics, ,2,18 provides much more epidemiologic information than identifying it as "pseudomonas
species."
Each hospital microbiology laboratory should maintain the capability of identifying gram-negative organisms to the genus level with at least 95% accuracy;
and such isolates from adequately collected and transported specimens and especially from serious infections, as those involving blood or cerebrospinal
fluid, should be speciated whenever possible. (The
problems of evaluation and speciation of mixed cultures have been the subject of several recent communications.3'4,35, 'i8) Species should be determined by
biochemical characterization, not by colonial morphology. Some hospitals may find it advantageous to
employ commercial multi-test media " k i t s " for biochemical testing. 16 ' 25 ' 30 ' 34 ' 49,30 ' 38-60 Information about
various systems may be obtained from state public
health laboratories or from the Bureau of Laboratories, CDC. In addition, public health and other
reference laboratories can provide assistance in identifying unusual isolates.
Rapid dissemination of data from the microbiologist
to the clinician 8 may be facilitated by providing both
preliminary and final copies of culture results. To facilitate surveillance of nosocomial infections and of all
infections requiring isolation or notification of public
health authorities, a copy of positive culture results
should also be sent to the infection control nurse.
Reports of all positive blood, cerebrospinal fluid, and
tuberculosis smears and cultures should be telephoned immediately to the appropriate clinicians and
to infection control personnel.
Antibiotic Susceptibility
Testing
The "Kirby-Bauer" single-disk diffusion method 6 12-14,66 o r a n equivalent test system is recommended
for antibiotic sensitivity testing. The epidemiologic
value of sensitivity patterns may be enhanced by
including certain antibiotics that do not necessarily
provide clinically useful information. For this reason
the Bacterial Diseases Division, CDC, currently
recommends that two disk sets, of 12 antibiotics
each, be used; one set is for gram-negative and the
A.J.C.P. • February 1978
other for gram-positive aerobic isolates.* While alternative sets, employing fewer disks, have been advocated
for routine clinical use, 44 the few extra disks selected
here primarily for epidemiologic purposes are inexpensive, and all 12 disks can be placed in the same
dispenser and applied simultaneously to one agar plate.
Moreover, while the results from a limited disk set
allow treatment decisions for individual patients, the
results from the additional disks have proved valuable
to some institutions in identifying and evaluating
episodes of cross-infection and common-source infection. Results from these disks have also been helpful
in tracing low-frequency infections occurring in many
different hospitals. For example, during a recent
nationwide outbreak of bacteremia, susceptibility of
Enterobacter agglomerans blood isolates to nitrofurantoin and naladixic acid assisted in identifying
epidemic strains from contaminated commercial intravenous products. 39 Furthermore, comparison of the
expected and observed susceptibility patterns for
organisms can provide valuable taxonomic and quality
control information.46
At least annually, in cooperation with the infection
control committee, the laboratory should distribute
to all clinicians a summary of sensitivity patterns
for various sites and major pathogens. The infection
control committee and/or a medical staff committee
may wish to review antibiotic utilization at this
time. 3757 ' 71 Furthermore, if a list of the cost (per
unit dose) of each antibiotic is included in the
summary, clinicians may be motivated and assisted
in reducing costs for patient care. The infection
control committee may decide not to include in
clinical reports the results of sensitivities performed
for epidemiologic purposes only or those performed
on antibiotics the hospital wishes to control. When
this is the case, clinicians should be informed of
which antibiotics are being tested routinely but not
reported.
Retrievable Laboratory
Records
Laboratory records should be retained at least
2 - 3 years to facilitate retrospective epidemiologic
investigations and use of laboratory data for qualitycontrol activities. Culture data for inpatients and outpatients should be maintained separately and should
be recorded so that results are readily available
by type of specimen, pathogen, and date. The source
of each specimen, the date of collection, the pa* The gram-negative set should contain: nitrofurantoin, chloramphenicol, amikacin, trimethoprim-sulfamethoxazole, cephalothin, tetracycline, gentamicin, naladixic acid, ampicillin, colistin,
carbenicillin, and kanamycin. The gram-positive set should contain:
penicillin, clindamycin, cephalothin, streptomycin, erythromycin,
sulfathiazole, vancomycin, chloramphenicol, tetracycline, methicillin, kanamycin, and neomycin.
Vol. 69 • No. 2
ROLE OF THE LABORATORY IN INFECTION CONTROL
tient's name, hospital number, hospital service, and
ward, and the final isolate identification(s) should be
recorded. The results of antimicrobial sensitivity
tests and any special biochemical (or typing) reactions may also be entered. Bound log books for
each major type of specimen (blood, wound and
skin, cerebrospinal fluid, urine, stool, sputum and
respiratory, and other) provide simple, inexpensive,
and epidemiologically useful records. Sole reliance on
a filing system of loose laboratory slips is not
recommended, since specific data are difficult to retrieve and are easily lost. When available, computer
storage of all results is advantageous—though
non-computerized rapid retrieval and sorting systems
may also be useful.53
Quality Control
Participating in proficiency testing programs helps
the laboratory maintain competence, particularly when
proficiency test specimens are submitted to the laboratory in a blind fashion and are handled routinely.
Hospital-supported, continuing education is very important for "personnel quality control"—particularly
if small laboratories are to remain abreast of technological advances. 21 In addition to these and the
other quality control activities that are discussed
above, selected laboratory materials, media, and
methods may be examined periodically."••43-48-51 The
Manual for Quality Control Procedures for Microbiological Laboratories,19 available from the CDC
Bureau of Laboratories, offers a comprehensive discussion of this subject.
Despite quality control within the laboratory,
erroneous microbiology results related to the inadvertent use of faulty or contaminated materials
outside the laboratory may be overlooked by both
clinician and microbiologist. For instance, an "outbreak" of false-positive Gram stains of cerebrospinal
fluid was recently caused by nonviable contaminants
in the specimen tubes in a lot of commercial
lumbar puncture trays. 69 Similarly, contaminated
skin antiseptics, Vacutainer tubes, penicillinase, and
blood culture media have all been implicated in
outbreaks of pseudobacteremia. 9,12,38,45 Such sources
of error should be considered when culture or stain
results do not appear to reflect clinical or epidemiologic
findings accurately.
Microbiologic Sampling and the Investigation
Nosocomial Outbreaks
of
When microbiology personnel are asked for advice
about microbiologic sampling, they should be prepared to recommend methods for culturing, and
they should also be prepared to recommend who and
133
what should (and should not) be sampled. In the
absence of an epidemic situation, sampling should
be minimal. All steam and ethylene-oxide-gas sterilizers should be checked at least once each week
with a suitable live-spore preparation; 5 ethylene-oxidegas sterilizers should also be checked with each
load of items that will come into contact with blood
or other tissues. Hospital-prepared infant formulas
should be cultured each week. Instruments that
touch mucous membranes but are disinfected rather
than sterilized before use, such as inhalation and
anesthesia equipment and endoscopes, may be
sampled on a spot-check basis as needed to insure
adequacy of disinfection. Although commercial patient-care items labeled sterile (such as intravascular
catheters and fluids) have occasionally been contaminated with viable organisms that can cause patient disease, routine sampling of these items is not
recommended because of the low frequency of contamination and because of the difficulty and expense
of performing adequate sterility testing. When contamination of commercial products sold as sterile is
suspected, the Food and Drug Administration should
be telephoned immediately.
Some hospitals may occasionally do limited environmental microbial sampling for educational or housekeeping quality control purposes. However, levels of
environmental contamination in hospitals have not
been shown to correlate with the incidence of nosocomial disease, and CDC and the American Hospital
Association therefore discourage routine environmental sampling.1-61 In-use testing of disinfectants
and antiseptics is not recommended, and, furthermore, routine culturing of patients or hospital personnel for microbial carriage is not generally
recommended.
The investigation of an outbreak, however, often
necessitates that many cultures be taken from patients, personnel, and the environment, and laboratory personnel should be prepared to recommend the
most appropriate culturing procedures. 1 - 5 When patients and personnel are evaluated for microbial
carriage, the culture medium is determined by the
epidemic pathogen, and the sites to be cultured may
include nasopharynx, throat, umbilicus, groin, rectum,
vagina, skin lesions, and hands. Identification of all
infected and colonized individuals may be of utmost
importance in outbreaks where treatment of carriers
or cohorting of affected persons is felt to be a
keystone in control. However, culture surveys of
patients, and especially of personnel, may be extensive and should be undertaken only when indicated
as necessary by epidemiologic findings, and then
carefully planned.1-27
During outbreaks, samples may also need to be
134
WEINSTEIN AND MALLISON
taken from objects that appear to be epidemiologic a l ^ implicated in the spread of infections, such
as patient-care supplies or equipment, medicines, antiseptics, soap dispensers, lubricants, hand lotions,
food, kitchen equipment, water, ice, and air. While
there are no standard technics for culturing many of
these objects, there are definitely good and bad
approaches. The guidelines given below should be
helpful in most situations; however, when questions
arise it is best to consult a public health or other
reference laboratory before undertaking any large
survey that might produce misleading information.
Many objects may be cultured by premoistened
swab of, careful rinse with, or immersion in brainheart infusion broth enriched with 0.5% beef extract.
Whenever the object being cultured may contain
residual disinfectant, the broth should contain 0.07%
lecithin and 0.5% Polysorbate-80 as neutralizers.
The initial broth culture may be allowed both a 4- and
a 24-hour enrichment period before being plated onto
agar appropriate for the isolation of the implicated
pathogen(s). When necessary, the enrichment broth
can be modified for specific epidemic pathogens (for
example, tetrathionate brilliant green broth would be
most appropriate for salmonella enrichment), and the
enrichment and isolation procedures may be adapted
for quantification. 3 Samples of water or (melted) ice
may be cultured by passing the suspect fluid through
a .45-/xm (or .22-^u,m) Millipore filter and then culturing
the filter in broth or directly on agar. Air sampling
may be performed with either settling plates or sophisticated instruments. 20 However, air-borne spread of
nosocomial bacterial infections is probably very uncommon and, when suspected, should be evaluated
by someone with experience in this field. Sampling
of suspect intravenous fluids (or blood products)
requires careful aseptic technic and is described
elsewhere. 5,24
During culture surveys, unusual characteristics of
epidemic isolates, such as resistance to multiple
antibiotics or heavy metals, may enable these organisms to grow selectively on a specially prepared
medium incorporating antimicrobial agents (thus decreasing the effort and time required to work up
specimens from the survey). Laboratory personnel
should be prepared to make and pretest such media
as needed. 3,52 Epidemiologically important isolates
may need special typing and, if so, should be forwarded to state or local reference laboratories.t Although hospital laboratory personnel may not have the
facilities to perform specialized typing procedures,
they should know which organisms are typable 28
t The current federal regulations for packaging etiologic agents
for air transport may be obtained from the Office of Biosafety,
CDC.
A.J.C.P. • February 1978
and which laboratories can perform the procedures.
Furthermore, in cooperation with infection control
personnel, the laboratory personnel should subculture
and save epidemiologically important isolates, whether
such isolates are from outbreaks or from single cases
of unusual or potentially epidemic diseases. A system
for reviewing and periodically discarding these isolates must of course also be set up. Finally, to
facilitate all the microbiologic activities that are
necessitated by an outbreak, the laboratory (or
Infection Control Committee) should have a contingency fund to enable personnel, materials, and
space to be temporarily assigned to epidemic aid
support. Individual patients should not bear the
cost of the contingency fund; rather, costs to the
laboratory of investigating an epidemic, as well as
costs of laboratory inovations that are discussed
in this paper, should be evaluated by hospital
administration in arriving at basic charges for all
patients.
Prevention of Laboratory-acquired Infection
Because of the possibility for frequent contact
between laboratory personnel and infectious materials,
infection control within the microbiology laboratory
is an important, although often overlooked, aspect
of hospital infection control. The infectious materials
in any laboratory will vary depending on the prevalence of various pathogens in the hospital, on the
extent to which the laboratory attempts to isolate
viral, fungal, or mycobacterial organisms, and on the
nature of any research undertaken. However, despite
institutional variations, several general comments
can be made regarding prevention and control of
laboratory-acquired infections.
Nationwide, the three most common causes of
laboratory-acquired infections, accounting for approximately a third of known cases, are hepatitis (a particular problem with glassware washers and other
laboratory workers who come in contact with blood),
tuberculosis, and brucellosis. 26,47,64,63 In addition,
etiologic agents of shigellosis, tularemia, psittacosis,
Q fever, amebiasis, and especially coccidioidomycosis,
although infrequently encountered in many laboratories, are infectious enough to be considered among
the next most common causes of reported laboratoryacquired disease. The extents to which other agents
may cause inapparent or seemingly non-laboratoryrelated infections, which can only be measured by
surveying laboratory workers periodically for seroconversion or recent infectious illness, are not known;
however, experiences with hepatitis B suggest that
seroconversion to some organisms may be quite
extensive before it is detected.
Vol. 69 . No. 2
ROLE OF THE LABORATORY IN INFECTION CONTROL
Excessive exposure to infectious material occurs
most frequently because of accidents involving needles
and syringes, broken glassware, or spilled cultures. 2 "- 47 " 2 " 4 Accidental puncture of skin with a contaminated needle is, of course, a hazard to any hospital employee. In addition, in the laboratory, infectious aerosols may be unwittingly created when
syringes are used improperly."4 Because of this hazard,
clotted blood or pus should not be homogenized
through a needle, and only Luer-lock syringes should
be used in the laboratory. Moreover, when air bubbles
are being expelled from a syringe or when a needle
is being withdrawn through the stopper of a culture
or vaccine bottle, an alcohol-soaked cotton ball should
be used to shield the needle.
Pipettes may also transmit diseases in the laboratory. 10 " 4 In addition to the obvious risk created by
mouth-pipetting or improper disposal of contaminated
pipettes, infectious aerosols may be created when
the contents of a pipette, even the last drops, are
forcibly expelled. Aerosols may also be liberated
when infectious materials are macerated, ground,
blended, or centrifuged, and when ampules of lyophilized bacteria or viruses are opened.47-62-64
All new laboratory personnel should be familiarized
with the hazards of disease transmission within the
laboratory. It is hoped that an introductory course on
laboratory safety will encourage good technic and help
personnel to understand the rules prohibiting mouthpipetting, drinking, smoking, and eating in the laboratory and the rules requiring handwashing, adequate
waste disposal, surface decontamination, and the use
of protective clothing, safety cabinets, and hoods. A
reference source for decontamination methods within
the laboratory and for the types of precautions
necessary for different organisms and procedures is
available from the CDC Office of Biosafety.11
To assess the adequacy of infection control within
the laboratory, the health of laboratory personnel
should be monitored routinely. Staff should be given
pre-employment and at least annual skin tests for
tuberculosis, followed by chest x-rays when indicated. Periodic screening of laboratory personnel for
hepatitis-B antigen seroconversion may be helpful in
determining high-risk areas in the laboratory. In
general, a log of all laboratory accidents and their
outcomes should be kept, work habits should be discussed with accident-prone employees, 29 and the
possibility of laboratory-acquired disease should be
considered whenever personnel develop unusual infectious illnesses.
Acknowledgments.
The experiences of many past and present
members of the Hospital Infections Branch and Epidemiologic
Investigations Lab Branch, Bureau of Epidemiology, CDC, as well
as the authors' experiences with a large group of hospitals that
135
have cooperated with the CDC's program for national surveillance
of nosocomial infections, have been invaluable in the preparation
of this manuscript.
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