Biomedical Engineering Reference
In-Depth Information
backgrounds and should include animal care staff that
perform the daily care of the nonhuman primates colony.
An excellent source for guidelines and information on
performing an effective risk assessment is included in the
ILAR publication Occupational Health and Safety in the
Care and Use of Nonhuman Primates (
Murphy and Rob-
erts, 2003
). Essentially, a thorough evaluation of the risks
associated with the tasks to be performed must be followed
by a complete integration of the means of reducing or
controlling exposure to the identified risks. The means of
controlling or reducing the risks include design elements
such as air-flow, use of biosafety cabinets, and cage design.
Additional components of the program such as personal
protective equipment (PPE) and administrative controls are
all a part of an effective program of risk management. The
approach to all risks should be reasonably uniform and an
integral part of the occupational health program of the
facility.
tuberculosis) may have multiple routes by which infection
may occur.
Transmission patterns of infectious agents are typi-
cally the same in research facilities as in the community.
For example, bacterial enteric pathogens typically
produce infection following the ingestion of relatively
large numbers of viable organisms in both settings.
Ordinary laboratory manipulations of clinical specimens
and cultures of these agents pose no demonstrated hazard
of infection via the respiratory route. Consistent use of
common sense, good laboratory practices, and personal
protective equipment such as those described and rec-
ommended for Animal Biosafety Level 2 can prevent
occupational infections from bacterial enteric pathogens
and most primary pathogens. Consistent use of the simple
practice of hand washing would prevent many of these
infections.
Mycobacterium tuberculosis is representative of agents
for which Biosafety Level 3 practices, containment
equipment, and facilities are recommended. This agent is
prevalent in certain communities and is commonly
cultured in clinical laboratories. Exposure in the
community and laboratory is primarily via inhalation of
infectious droplet nuclei, which typically contain one or
only a limited number of viable tubercle bacilli. All
manipulations of clinical materials, tissues, cultures, or
infected animals may generate infectious aerosols.
Consequently, the good laboratory practices and personal
protective equipment recommended for Biosafety Level 2,
supplemented by the regular use of primary containment
equipment (biological safety cabinets (BSC)) and engi-
neering controls (directional and nonrecirculating venti-
lation systems), are essential to work safely with this
agent.
For some infectious agents, the usual route of infection
in the laboratory animal facility may vary considerably
from that normally observed in the community. The rick-
ettsiae and arboviruses, typically transmitted by arthropod
vectors in nature, are often transmitted in the laboratory via
aerosol or accidental parenteral inoculation.
In general, those agents that may be transmitted by
multiple routes, especially by inhalation, pose significantly
greater occupational infection risks than those with only
a single portal of entry.
History of Occupational Infection
Much of the information on occupational infections is
anecdotal and incomplete. Rates are lacking. Reported
cases, or the absence of reported cases, are nevertheless
important indicators of occupational infection risks. The
series of surveillance summaries by
Pike (1976)
document
the continuing hazard of such infections as tuberculosis,
shigellosis, and hepatitis A and B as well as a number of
other infections caused by less prevalent agents.
In contrast, the absence of any documented cases of
occupationally transmitted cases of Creutzfeldt
e
Jakob
disease (CJD) and the fewer than 30 reported cases of
occupationally associated human acquired immunodefi-
ciency virus infection strongly support the conclusion that
these agents pose low occupational infection risks, despite
the grave consequences should infection occur. A similar
point can be made regarding the fewer than 30 cases of B
virus reported in the world literature since 1932. The fatal
consequences of B virus infection, however, complicate an
objective risk assessment of this sporadic, obscure, and
poorly defined disease.
Documented infections and disease outcome in labo-
ratory, animal care, and healthcare personnel may provide
meaningful information on agent and disease-specific
occupational risks. The importance of a single case of
occupation-associated disease must be cautiously evaluated
as an indicator of occupational risk to infectious diseases.
Infective Dose
The infective dose, or more specifically the ID
50
, is the
estimated number of organisms or virus particles required
to produce infection in 50% of normal adult humans
exposed by a given route. This number may vary widely
with the route of infection, the immune status of the
exposed person, and the strain of the challenge organism.
Hepatitis B virus (HBV), many of the arboviruses, and the
Route of Infection
The route of infection of specific agents is perhaps the
single most important indicator of occupational infection
risk to personnel working in laboratory and animal
research facilities. Some agents (Plasmodium spp.) may
have only a single portal of entry whereas others (e.g.
