Recent concerns about the clinical relevance of susceptibility testing echo those expressed previously by a number of authors.’-” These concerns are well founded and are perhaps even more important today because of the proliferation of new antibiotics and the changes in reimbursement philosophy.” Ultimately, the question becomes that raised by David Greenwood: “In vitro veritas?” The following discussion will review the role of susceptibility testing in clinical medicine with emphasis on myth versus reality. In addition, new directions for susceptibility testing that promise increased clinical relevance will be covered.

During the course of a tuberculosis skin testing program at a chronic care Veterans Administration Medical Center, we uncovered evidence of occult transmission of endemic tuberculosis. Skin test conversion of eight patients (one of whom had unsuspected progressive primary tuberculosis) and two employees was ultimately traced to a patient in whom tuberculosis was first diagnosed at autopsy three years earlier. Identification of employee skin test conversions was a key factor in recognizing and terminating disease transmission. Throughout the institution, 33% of patients were tuberculin-positive; 10.8% demonstrated the booster phenomenon after initial negative skin tests. Prevalence of tuberculin positivity among employees was 28%. Twelve percent of initially tuberculin-negative employees converted during employment. Our experience documents the value of tuberculin testing of both patients and staff in a chronic care environment, and the necessity of vigorous investigation of skin test conversions.

The incidence of hacteriuria, significant urinary tract infection, and cost associated with the use of two urinary catheter drainage systems were evaluated in a population of hospitalized adult males. A commercially available device comprised of a Foley catheter attached with a heat-shrunk plastic seal to the tubing of a closed drainage hag (preconnected system) was compared with a standard system that had the Foley catheter attached to the closed drainage hag after it had been inserted. Using a randomized prospective design, the performance of the preconnected system in 97 patients was compared with that of the standard system in 105 patients. Catheters were left in place a mean of 6.4 and 7.6 days in the respective groups. Bacteriuria occurred after catheter insertion in 11.3% of patients receiving the preconnected system and 13.3% of patients receiving the standard system (not statistically significant). When bacteriuria developed, it occurred within seven days of catheter insertion in 50% of instances, irrespective of drainage system employed, suggesting that manipulations related to catheter insertion were important in initiating bacteriuria. Significant urinary tract infections occurred in only 2% of all patients studied. The higher cost for purchasing the preconnected system was not warranted for the population of patients studied.

Nine hundred seventy-two cultures taken from the external nares and the vaginal vestibules of 54 women for the isolation of Staphylococcus aureus were studied. The swabs were plated directly to a trypticase soy agar plate containing 5% sheep blood and were then placed into a selective staphylococcal broth. Both culture methods were compared for the ability to recover S aureus.

Twenty percent (26/131) and 66% (38/58) of the S aureus-positive cultures taken from the nares and vagina respectively were cultured from the selective broth only. We believe that a selective staphylococcal broth should be used in addition to routine culture techniques to isolate S aureus from infection control surveillance cultures.

Medical care has come a long way in the last century. People live longer; deadly diseases are prevented, cured, or ameliorated. In short, medical care is more effective than at any previous time. In this sense, effectiveness is a straightforward concept that measures changes in life expectancy, quality of life, and occurrence of disease. Effectiveness is sometimes difficult to quantitate; yet it is an important part of clinical decision making. For example, is the use of universal precautions effective in preventing the spread of the human immunodeficiency virus? Is antibiotic prophylaxis effective in preventing postoperative wound infections? Is chest percussion effective in the therapy of' pneumonia? Is a brain biopsy more effective than empiric therapy in treating encephalitis?

In a one-year retrospective review, 138 symptomatic infections were identified in 145 admissions to a rehabilitation unit. One hundred twenty-six (91%) infections were either urinary or skin and soft tissue infections. The daily incidence of infection increased with increasing numbers of infections for infected patients. Patient factors associated with infection included male sex, young age, spinal cord injury, admission for management of decubitus ulcers or urinary infection, history of urinary infection, urologic interventions or skin breakdown, and bladder and bowel incontinence. All patients with a history of chronic urinary infection or skin breakdown developed infection. In a logistic regression model, factors that were independently associated with risk of infection in the remaining patients included sex, incontinence, chronic neurologic disease, and prior urologic interventions. This review suggests rehabilitation patients are at high risk of acquiring nosocomial infection. The subgroup of patients with the highest risk of infection are identifiable by specific characteristics.

Hospitals, insurance companies, and federal and state governments are increasingly concerned about reducing patient cost expenditures while maintaining high quality patient care. One method of reducing expenditures has been to tie hospital reimbursement with a prospective payment system based on diagnosis-related groups (DRGs). However, reimbursement under the DRG system is not acceptable for all patients in all hospitals because it is neither an accurate predictor of costs nor of clinical outcome. This deficiency poses significant problems for hospitals because DRGs are used nationwide as the prospective payment system for inpatients covered by Medicare. Several case-mix adjusters have been proposed to modify DRGs to improve their accuracy in predicting costs and outcome. We reviewed five of the most widely available indices: Acute Physiologic and Chronic Health Evaluation (APACHE II), Coded Disease Staging, Computerized Severity Index (CSI), Medical Illness Severity Group System (MEDISGROUPS), and Patient Management Categories (PMC). Recommendations for the use of a single case-mix adjuster cannot be made at this time because all indices have not been compared in sufficiently diverse settings and because some are better predictors of costs while others are better predictors of clinical outcome. Hospital epidemiologists and other infection control practitioners should be informed about these indices and their potential applications as they expand their role beyond infection control problems to issues concerning cost containment, quality assurance, and reimbursement.

Malassezia furfur, a lipophilic yeast, has become recognized as a cause of sepsis in infants receiving parenteral fat emulsions via indwelling deep venous catheters. Colonization of infants' skin may be a prerequisite to colonization of the intravascular catheter and subsequent infection with M furfur. Three hundred ninety-three surveillance cultures were performed on 146 infants during their first 12 weeks of hospitalization in the intensive care unit (ICU) or the neonatal transitional unit (NTU). In addition, 47 full-term newborn infants and 38 healthy infants in the well-baby clinic were cultured. Colonization rates were greatest (48%) during the second month of hospitalization for the infants in the ICU/NTU group. In contrast, 0 of 47 newborn infants and 2 of 38 healthy infants were colonized. Prematurity and a prolonged length of stay were identified as risk factors for colonization.

This is the second in a series of articles addressing legal issues in infection control. The first article (Infect Control Hosp Epidemiol 1988: 9(3):127-129) discussed the basic elements of liability law as it relates to infection control in the hospital setting. This article will focus on confidentiality in the infection control process.

Infection monitoring and control, as it occurs in most hospital settings, depends on ready access to relevant information, careful evaluation of the data, and appropriate communication of conclusions and recommendations. Equally obvious, however, is the risk associated with free-floating information of this significance. Infection control programs produce a multitude of documents that are of potential interest to outsiders such as fellow staff members, other health care institutions, and attorneys. Without specific attention to mechanisms for protecting its confidentiality, information gathered in the infection control process may well become available to some or all of those interested parties.

For years, Infection Control Practitioners have been asked to identify the “ultimate” hospital::: disinfectant. Health care personnel seem to want a multipurpose product; one that can he used for handwashing for, instrument disinfection and for cleaning the commode. Simply stated, there is not one product that call successfully do all three. Antiseptic solutions, which are approved by the Food and Drug Administration are for use on skin (ie, handwashing and skirt preparation whereas disinfectants are for use in the inanimate environment and are approved by the Environmental Protection Agency.

There are two classifications of' disinfectants housekeeping disinfectants and instrument disinfectants. Housekeeping disinfectants are generally low-level disinfectants, and quartenary ammonium compounds or phenol-based solutions are the most common. Instrument disinfectants are high-level disinfectants such as glutaraldehydes and chlorine dioxide.

An infection rate was calculated for all subclavian catheters inserted during a 12-month period. The overall, single lumen, and triple lumen infection rates were 1.7% (42/2,431), 0.4% (8/1,936), and 6.9% (34/495), respectively. After excluding single lumen catheters in patients in a surgical cardiovascular unit who appeared to have a decreased risk of infection, the overall, single lumen, and triple lumen rates were 3.7% (42/1,140), 1.2% (8/645), and 6.9% (34/495), respectively. Within this group, 11.8% (281237) of the catheters used for total parenteral nutrition (TPN) were infected, whereas 1.6% (14/903) of the non-TPN catheters were infected. Of patients receiving total parental nutrition through a triple lumen catheter, 14.5% (25/172) became infected, whereas 4.6% (3/65) of the patients receiving total parental nutrition through a single lumen catheter became infected. Single and triple lumen patient groups appeared comparable based on average age, death rate, immunosuppression, underlying disease, and duration of catheterization, but the risk of infection was approximately three times greater for patients receiving total parental nutrition through a triple lumen catheter.

A recent article in this section reviewed some problem areas of susceptibility testing. In particular, the “myth” of susceptibility testing being predictive of clinical outcome was discussed. The realization of this myth often leaves clinicians less comfortable when selecting antimicrobial agents. The question they often ask is, “How does one select antibiotics?” This question has always been important for empiric therapy of the septic patient. It has become even more important in the cost containment era. The introduction of new antimicrobial agents that are very costly when compared with older agents has greatly complicated antimicrobial therapy. It is now possible to use antibiotics correctly in a therapeutic sense, but to misuse them in an economic sense. Nonetheless, recognition of new pathogens, increasing resistance of pathogens to older antimicrobial agents and more complicated clinical problems have increased the need for these new agents. The following discussion will focus on those factors upon which the selection of a specific antimicrobial agent (or combination of agents) is based, the least of which should be the results of susceptibility tests.

Much of clinical and hospital epidemiology involves the identification and enumeration of cases or the comparison of case frequencies between two or more groups of interest. Because both of these activities involve the use of statistics, it is important to pay careful attention to biostatistical issues involved in the collection and the analysis of such data.

In this article, the first in a series of biostatistical papers, we discuss some general issues that are important in the design, analysis, and interpretation of clinical epidemiologic data. Subsequent papers in this series will deal with specific methods of analysis, examples of these methods of analysis, and limitations and interpretations of the methods.