Epidemiology 101: Surveying the Scene

ByKris Ellis

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

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

Epidemiology gives the ICP tools to evaluate infections intheir practice, says Loretta Litz Fauerbach, MS, CIC, director of infectioncontrol at Shands Hospital at the University of Florida. Throughpopulation-based analysis, the ICP can help determine significant trends andpotential areas for intervention.

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

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


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

With regard to nosocomial infections, SHEAs reportrecommends incorporating several elements into the surveillance process,including:

  • Identification and description of the problem or event to be studied

  • Definition of the population at risk

  • Selection of theappropriate 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

  • Selectionof specifc events to be monitored should be guided by validated, nationallyavailable benchmarks appropriately adjusted for patient risks so that meaningfulcomparisons can be made.

The report also notes that a well-designed surveillance effortis a necessity for an effective infection control program and in promotingimproved patient care.

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

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

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

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


In many settings, especially larger facilities and systems,infection control and epidemiology are dependent upon the cooperation andcollaboration between several key positions. Infection control professionals,medical epidemiologists and support staff form the core of the institutionsprimary response, says Fauerbach. Traditionally, the hospitalepidemiologist is an infectious disease physician by training. The hospitalepidemiologist usually also has a medical practice devoted to taking care ofpatients. In many facilities the epidemiologist may only be part-time, or inmany smaller community-based healthcare facilities there is no hospitalepidemiologist. The hospital epidemiologist brings special medical skills andevaluation 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 largerfacility, they may have a full-time healthcare epidemiologist on staff. Itsimportant to note that even among the healthcare epidemiologists, and I thinkmost of those positions are occupied by physicians, usually infectious diseasephysicians, theres a real variety of epidemiologic training even among thosefolks. So, in some settings, the healthcare epidemiologist is maybesomeone who is very skilled in infectious diseases but they may not have anyformal training in epidemiology.

Regardless of the specific situation and training levels,infection control and epidemiological personnel are devoted to the common goalof promoting safety and protecting patients. The whole field is, of course,termed healthcare epidemiology and infection control, so in general there isvery close partnering of the work that the infection control professional isdoing 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 servesas the facilitys healthcare epidemiologist. When the titles are split, itscrucial that they work closely together and inevitably they do.

Meeting the Challenge

ICPs who handle all epidemiological duties in a facility mayfeel a bit overwhelmed by this aspect of the job, but Srinivasan emphasizesagain that the basic principles are oftentimes sufficient and should beembraced. The message there is primarily not to be afraid of usingepidemiology, he says. Sometimes people are afraid because they think, Idont have formal epidemiology training, or, I dont know very muchabout statistics. I think the important thing to remember is that you dontnecessarily need all of that to do the basics of an investigation. He alsoreiterates that the creation of a basic line list is a significant step that canbe very valuable in an investigation.

APIC states that practice standards for infectionsurveillance, prevention and control (ISPC) should apply epidemiologicprinciples and statistical methods such as risk stratification, trend analysisand identification of target populations.2 APICs standards also cite thefollowing criteria with regard to epidemiological practices:

  • Conducts surveillance and investigations by usingepidemiologic principles

  • Uses appropriate statistical techniques to describethe data, calculate rates and critically evaluate significance of findings

Avariety of opportunities exist for those who wish to increase theirepidemiological knowledge level. Srinivasan recommends the SHEA/ CDC Course inHospital Epidemiology. Its usually hosted twice a year in different placesthroughout the country and its a very good overview of some of the basicepidemiology and statistical methods for doing healthcare epidemiology and thatsalso a very nice resource for people, he says.

From an infection control perspective, the effectiveness ofapplying epidemiologic principles can oftentimes be measured directly. Forexample, Fauerbach explains how such methods have been valuable in her facilitysefforts to decrease central line-associated infections. We have been able tomeasure the initial rate and then the impact of each intervention, she says. We were able to prove that certain interventionsproduced statistically significant decreases in rates and lead to betterpatient outcomes and improved patient safety. Most recently, we have validatedthe use of Chloroprep (2 percent chlorhexidene gluconate plus alcohol) as a skinprep and the positive effect of BioPatch® (chlorhexidene gluconate impregnatedpatch). The combination demonstrated a 31 percent decrease in central venouscatheter-associated infections (p < 0.01).

Successes such as these justify the tireless efforts of ICPsto improve patient care and help facilities realize the cost benefitsassociated with infection control. Fauerbach notes that epidemiology gives thehealthcare institution confidence in its ability to track trends and interveneappropriately. It assures that data is comparable by the use of definitionsand pre-determined methodology of data collection and analysis, she says. Epidemiologicalmethods provide infection control programs with the tools to identify problems,design interventions to improve patient outcomes, and to validate interventions.

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