January 1, 2005

Epidemiology 101: Surveying the Scene

Kris Ellis

The primary goals of any effective
infection control program include the protection of patients, healthcare workers
(HCWs) and all others who work in or visit the healthcare environment. Infection
control practitioners (ICPs) must focus their attention and energies on a
variety of different facets of the setting in which they practice in order to
accomplish these goals. Epidemiologic principles and methods constitute an
essential aspect of infection and outbreak control that ICPs can use to improve
the quality of care in their facilities.

At its core, epidemiology seeks to determine and understand
the causes of disease among a defined population through the application and
analysis of relevant data and statistics. Whether the population in question is
large or small, sound epidemiologic methods can provide a structured,
disciplined approach to the investigative process. In the healthcare
environment, where time and efficiency are of the essence, this type of
approach can offer many advantages.

Epidemiology gives the ICP tools to evaluate infections in
their practice, says Loretta Litz Fauerbach, MS, CIC, director of infection
control at Shands Hospital at the University of Florida. Through
population-based analysis, the ICP can help determine significant trends and
potential areas for intervention.

In the midst of an outbreak, it is important to have a
systematic and consistent method of sorting out what can be a complex and
confusing situation.

I think its almost impossible to over-emphasize the
importance of old-fashioned, what we call shoe leather epidemiology in
terms of looking for causes of healthcare-associated outbreaks of infections, says Arjun Srinivasan, MD, medical epidemiologist with the
Division of Healthcare Quality Promotion at the Centers for Disease Control and
Prevention (CDC). Given how complicated looking at these infections is, its
literally impossible to try and do things like culturing of every potential
thing that could be contaminated or explore every potential route of infection,
so its really the epidemiology that is the primary step in guiding you toward
the most likely explanations for the infection.


In order to incorporate meaningful data into a facilitys
epidemiology and infection control efforts, accurate data collection and
management must be conducted on a regular basis. The Society for Healthcare
Epidemiology of America (SHEA) suggests that surveillance of adverse events is
the single most important aspect of data management in which a facility can engage.1

With regard to nosocomial infections, SHEAs report
recommends incorporating several elements into the surveillance process,

  • Identification and description of the problem or event to be studied
  • Definition of the population at risk
  • Selection of the
    appropriate methods of measurement, including statistical tools and risk stratifications
  • Identification and description of data sources and data collection
    personnel and methods
  • Definition of numerators and denominators
  • Preparation and distribution of reports to appropriate groups and
  • Selection
    of specifc events to be monitored should be guided by validated, nationally
    available benchmarks appropriately adjusted for patient risks so that meaningful
    comparisons can be made.

The report also notes that a well-designed surveillance effort
is a necessity for an effective infection control program and in promoting
improved patient care.

Compiling large amounts of data is only useful when it is
accompanied by skilled analysis of the numbers, however. If an infection
control program just collects raw numbers, it may not be able to identify the
real cause for an increase in infections, Fauerbach points out. She explains that epidemiological tools can help the
infection control team identify statistically significant trends and compare
data in order to improve outcomes and identify the problems that need to be

Given the requisite number-crunching and the amount of
information involved, technology is a consideration ICPs should be aware of. There
are listservs which are very useful, says Srinivasan. A very good one that
people are probably all aware of is the one on the Association for Professionals
in Infection Control and Epidemiology (APIC)s Web site. Thats a very powerful tool for ICPs to have at their
disposal. If you only could have one piece of technology, thats an incredibly
powerful one to have because it gives you access to a world of information and
resources and expertise.

Other powerful tools designed to aid in surveillance and
epidemiology do exist, but Srinivasan explains that most are not yet a real
possibility for most facilities. There are now some automated systems for
doing healthcare surveillance there are some programs you can purchase which
look to be very good and look to be very promising in terms of the time that
they can save, he says. Theyre very exciting but theyre also very
expensive. I think that its going to be a while before we see these very
widely implemented in a lot of hospitals simply because of the cost.

Many times, however, incorporating an epidemiological approach
is not always an arduous and expensive process, as Srinivasan explains. I
think whats important to note is that were not necessarily talking about
very sophisticated epidemiology using complex statistical methods to determine
associations sometimes this is literally as simple as making a line list of
the patients who were involved, what infections they had, what people took care
of them or where they were in the hospital, he says. In many instances its those very simple epidemiologic
tools that are the most important and the most helpful in terms of getting to
the bottom of an outbreak.


In many settings, especially larger facilities and systems,
infection control and epidemiology are dependent upon the cooperation and
collaboration between several key positions. Infection control professionals,
medical epidemiologists and support staff form the core of the institutions
primary response, says Fauerbach. Traditionally, the hospital
epidemiologist is an infectious disease physician by training. The hospital
epidemiologist usually also has a medical practice devoted to taking care of
patients. In many facilities the epidemiologist may only be part-time, or in
many smaller community-based healthcare facilities there is no hospital
epidemiologist. The hospital epidemiologist brings special medical skills and
evaluation to the role of infection prevention and control.

I think a lot of that reflects the size of the facility,
Srinivasan says. Most of the time if they do have a slightly larger
facility, they may have a full-time healthcare epidemiologist on staff. Its
important to note that even among the healthcare epidemiologists, and I think
most of those positions are occupied by physicians, usually infectious disease
physicians, theres a real variety of epidemiologic training even among those
folks. So, in some settings, the healthcare epidemiologist is maybe
someone who is very skilled in infectious diseases but they may not have any
formal training in epidemiology.

Regardless of the specific situation and training levels,
infection control and epidemiological personnel are devoted to the common goal
of promoting safety and protecting patients. The whole field is, of course,
termed healthcare epidemiology and infection control, so in general there is
very close partnering of the work that the infection control professional is
doing along with what the healthcare epidemiologist for the facility is doing.
In some places, those positions are merged into one and in fact the ICP serves
as the facilitys healthcare epidemiologist. When the titles are split, its
crucial that they work closely together and inevitably they do.

Meeting the Challenge

ICPs who handle all epidemiological duties in a facility may
feel a bit overwhelmed by this aspect of the job, but Srinivasan emphasizes
again that the basic principles are oftentimes sufficient and should be
embraced. The message there is primarily not to be afraid of using
epidemiology, he says. Sometimes people are afraid because they think, I
dont have formal epidemiology training, or, I dont know very much
about statistics. I think the important thing to remember is that you dont
necessarily need all of that to do the basics of an investigation. He also
reiterates that the creation of a basic line list is a significant step that can
be very valuable in an investigation.

APIC states that practice standards for infection
surveillance, prevention and control (ISPC) should apply epidemiologic
principles and statistical methods such as risk stratification, trend analysis
and identification of target populations.2 APICs standards also cite the
following criteria with regard to epidemiological practices:

  • Conducts surveillance and investigations by using
    epidemiologic principles
  • Uses appropriate statistical techniques to describe
    the data, calculate rates and critically evaluate significance of findings

variety of opportunities exist for those who wish to increase their
epidemiological knowledge level. Srinivasan recommends the SHEA/ CDC Course in
Hospital Epidemiology. Its usually hosted twice a year in different places
throughout the country and its a very good overview of some of the basic
epidemiology and statistical methods for doing healthcare epidemiology and thats
also a very nice resource for people, he says.

From an infection control perspective, the effectiveness of
applying epidemiologic principles can oftentimes be measured directly. For
example, Fauerbach explains how such methods have been valuable in her facilitys
efforts to decrease central line-associated infections. We have been able to
measure the initial rate and then the impact of each intervention, she says. We were able to prove that certain interventions
produced statistically significant decreases in rates and lead to better
patient outcomes and improved patient safety. Most recently, we have validated
the use of Chloroprep (2 percent chlorhexidene gluconate plus alcohol) as a skin
prep and the positive effect of BioPatch® (chlorhexidene gluconate impregnated
patch). The combination demonstrated a 31 percent decrease in central venous
catheter-associated infections (p < 0.01).

Successes such as these justify the tireless efforts of ICPs
to improve patient care and help facilities realize the cost benefits
associated with infection control. Fauerbach notes that epidemiology gives the
healthcare institution confidence in its ability to track trends and intervene
appropriately. It assures that data is comparable by the use of definitions
and pre-determined methodology of data collection and analysis, she says. Epidemiological
methods provide infection control programs with the tools to identify problems,
design interventions to improve patient outcomes, and to validate interventions.