Richard E. Dixon

Indwelling arterial catheters as a source of nosocomial bacteremia. An outbreak caused by Flavobacterium Species.

Between mid-May and mid-October, 1973, 49 blood cultures from 14 patients in an intensive care unit were positive for flavobacterium species, Group II-b. We conducted an investigation to determine how patients were being infected with this unusual organism. Comparison of the 14 infected patients with 37 controls associated indwelling arterial catheters with subsequent flavobacterium bacteremia (p = 0.005). Risk of infection was greatest during the period in which blood gas determinations were done most frequently (the first three days of catheterization) and in which infected patients had more blood gas determinations than control patients with arterial catheters (p less than 0.05). Flavobacterium species was cultured from in-use arterial catheters, from stopcocks, and from ice in the intensive-care units ice machine; the catheters were probably contaminated by syringes that were cooled in ice before being used to obtain arterial specimens for blood gas determination. This outbreak calls attention to arterial monitoring systems as a potential source of nosocomial infection.

Contamination of Intravenous Infusion Fluid: Effects of Changing Administration Sets

Daily change of intravenous (i.v.) infusion administration sets has been recommended by the Center for Disease Control since 1973 to reduce the risk of infusion bacteremia. To evaluate this recommendation, we undertook a prospective, randomized, controlled trial that compared the rates of i.v.-associated bacteremia, in-use i.v. fluid contamination, and phlebitis in 300 patients whose administration sets were changed every 24 h with those in 300 patients whose administration sets were changed every 48 h. No i.v.-associated bacteremia occurred. Twelve of 600 infusions (2%) had positive infusion-fluid cultures: five in one group and seven in the other. Both groups had comparable rates of phlebitis. In this study population with low rates of fluid contamination, no benefit accrued from changing the administration sets every 24 h instead of every 48 h. In hospitals with low rates of fluid contamination, the routine changing of i.v. administration sets every 48 h will result in substantial financial savings.

Effect of Infections on Hospital Care

To determine research priorities in infectious diseases, the impact of infections on hospital care in the United States is estimated from the number of infectious diseases observed in hospitals that cooperate with the Center for Disease Control in surveillance of community-acquired and nosocomial infections. Each year, over 3 million community-acquired infections require persons to be hospitalized, and over 2 million nosocomial infections are acquired. Approximately 90% of the infections treated in hospitals are bacterial. These infections account for an estimated 29 million days of acute hospital care, which is approximately 10% of the patient days in United States acute-care hospitals. The direct hospitalization costs for treating infectious diseases are estimated to be over

Comparison of endemic and epidemic nosocomial infections

4.8 billion. Treatment of infectious diseases accounts for a major portion of hospital care in the United States.

Secular trends in nosocomial infections: 1970–1979

Epidemics account for a small proportion of preventable infections acquired in hospitals, but they have been important in defining sources, modes of spread, and methods for prevention and control of nosocomial infections. To characterize hospital-based epidemics, 265 consecutive outbreaks investigated by the Center for Disease Control between 1956 and 1979 were reviewed. Pseudoepidemics were found in 11 percent of the investigations, most often resulting from errors in processing microbiologic specimens or from surveillance artifacts. In 223 actual epidemics, the pathogens most commonly involved were Staphylococcus aureus (19 percent), tribe Klebsielleae (14 percent), Salmonella (13 percent), hepatitis B virus (8 percent), enteropathogenic Escherichia coli (5 percent), Pseudomonas (4 percent) and group A streptococci (4 percent). Sites of epidemic infection were closely linked to the responsible pathogens. Gastroenteritis (21 percent), skin infection (18 percent), bacteremia (12 percent), meningitis (11 percent) and hepatitis (10 percent), infrequent causes of endemic nosocomial infections, were frequently involved in epidemics. Over the 25-year period reviewed, staphylococcal epidemics and outbreaks of gastroenteritis due to Salmonella and Esch. coli declined in frequency and those due to gram-negative bacilli and hepatitis B virus increased. Since 1970, clusters of primary bacteremia were the most frequently investigated type of epidemic. Many epidemic strains of staphylococci obtained since 1975 or Enterobacteriaceae obtained since 1970 exhibited unusual drug resistance. Specific site-pathogen combinations were closely associated with characteristic reservoirs and modes of spread.

Control of influenza in the hospital.

Nosocomial infection data from a mean of 81 hospitals has been reported to the National Nosocomial Infections Study (NNIS) each year since 1970. Surveillance has been conducted by the hospitals on an average of 1.16 million patients annually. The median nosocomial infection rate is 341 per 10,000 patients discharged, ranging from 312 in 1970 to 358 in 1975. Since 1975, the rate has steadily declined to 329 in 1979. By category of hospital, infection rates for community-teaching and municipal hospitals have declined in recent years whereas those for community and university hospitals have not. Infection rates for patients on the surgical service have declined steadily since 1975 to the lowest levels reported, 457 per 10,000 surgical patients discharged in 1979, primarily due to a decrease in the rate of surgical wound infections. On obstetrics, infection rates have increased steadily since 1970, also primarily due to surgical wound infections. Bacteremias have increased in frequency, particularly those associated with infection at other sites. No major shifts have been noted in the relative frequency of the most common sites of infection or pathogens causing infections.

Forging the missing link in infection control

Nosocomial transmission of influenza has been reported infrequently; however, patients in general hospitals are often among the most susceptible to the complications of influenza infection. Hospital-acquired influenza may occur more often than is reported, but it may be recognized because of lack of diagnostic facilities or the time required for virus isolation and identification. Based on the mode of transmission in the hospital, the established reservoirs of influenza virus, and duration of virus shedding, isolating patients with influenza may occasionally be useful but restricting visitors is probably not required. Vaccinating hospital personnel with influenza vaccine and, if influenza A is prevalent, giving amantadine hydrochloride to high-risk patients or personnel should both be considered.

Klebsiella pneumoniae Pseudobacteremia Due to Cross-Contamination of A Radiometric Blood Culture Analyzer

From the Bacterial Diseases Division, Center for Infectious Disease, Centers for Disease Control, Public Health Service, U.S. Department of Health and Human Services, Atlanta, Georgia. Requests for reprints should be addressed to Dr. Richard E. Dixon, Hospital Infections Branch, Bacterial Diseases Division, Center for Infectious Disease, Centers for Disease Control, Atlanta, GA 30333. *‘Present address: Department of Medicine, Helene Fuld Medical Center, Trenton, Nj 08638, and the Department of Medicine, Hahnemann Medical College, Philadelphia, PA 18164. Infectious disease epidemiologists use the metaphor of a chain in describing the occurrence of infection. Three links comprise the chain: a virulent agent, a susceptible host and a mode of acquisition or transmission by which the host acquires the agent. The absence of even one link will break the chain, and infection will not occur. Programs to prevent infections are also like a chain, and the chain of prevention also has three links. The first link in the preventive medicine chain is the characterization of a disease problem in order to understand its attributes, causes, and effects. The second link comprises efforts to develop prevention and control techniques so that the effects of disease may be ameliorated. The third link involves the actual implementation of prevention and control programs among populations at risk, thereby reducing morbidity or mortality. Each link in the preventive medicine chain is crucial; unless each is strong, prevention will not occur. This is particularly true in our efforts to prevent and control nosocomial infections. Understanding nosocomial infections-link one-and knowing how to prevent them-link two-are of scant benefit unless the knowledge and understanding are translated into routine practice-the third link. Nor can any link be easily bypassed. Although we may understand the epidemiologic determinants of disease, we undertake a hazardous course if we choose to implement preventive measures without having first tested them to see if they are effective and efficient. Each link must also be forged by rigorous research. It is apparent that the first two links require careful clinical, laboratory, and epidemiologic investigation, but it is perhaps less readily obvious that the implementation phase of public health must also be based on sound research. It must be, however. The most vexing question for most persons involved in the day-to-day work of nosocomial infectioncontrol is not “What shall I do,” but it is, instead, “Knowing what needs to be done, how can I assure that it is done.” A single example will illustrate this point. Although we may debate the agent to use or the exact technique to employ, there is no debate that handwashing by hospital personnel is one of the most important routine practices to be followed in preventing spread of nosocomial infection. Although the need for handwashing has long been recognized, no well designed studies are available to assist infection control personnel in designing programs that will ensure that hospital personnel will, in fact, wash their hands. As a result, we who are responsible for implementing control programs must improvise techniques for encouraging handwashing without assurance that those techniques are likely to be effective. This International Conference on Nosocomial Infections is organized to survey the current state of the art of infection control: it is, therefore, appropriate to examine our progress in each of the three phases, or links, of implementing infection control programs. To

Epidemic infections in surgical patients

Blood isolates from 13 patients in one hospital were positive for Klebsiella pneumoniae over a two-week period. Vials of potassium chloride used in intravenous fluid admixture initially were suspected of being contaminated and thus causing the problem. However, a comparison of patients who had blood cultures positive for K. pneumoniae with control patients who had blood cultures negative for this organism during the same period identified no common features that would explain the increase in K. pneumoniae blood isolates. Careful evaluation of laboratory data suggested that six of the 13 culture-positive patients had probable pseudobacteremia, an explanation that would account for the increase in isolates above the endemic level of true K. pneumoniae bacteremia in the hospital. Epidemiologic data suggested that cross-contamination of adjacent and non-adjacent blood culture vials on the radiometric blood culture analyzer was the cause of pseudobacteremia; K. pneumoniae serotyping data supported this hypothesis. A mock trial using the analyzer demonstrated that cross-contamination of non-adjacent vials by the sampling needles could occur. Changing the sampling needles of the analyzer daily, in accordance with the manufacturers recommendations, prevented further episodes of pseudobacteremia from the analyzer.

Gentamicin treatment associated with later nosocomial gentamicin-resistant Serratia marcescens infections.

From 1967 to 1977, the Centers for Disease Control investigated 22 epidemics of nosocomial infections among surgical patients. Fifteen of the outbreaks involved operative site infections and were caused by various microorganisms: gram-positive bacteria (47%), gram-negative bacteria (13%), atypical mycobacteria (13%), Aspergillus (7%), and multiple microorganisms (20%). Sources for infecting strains were infected personnel or patients (53%), the operating room environment (20%), and four unknown factors (27%). Control measures included treatment of personnel who were carriers and infected patients, adherence to aseptic techniques, improvements in OR airflow and cleaning procedures, and discontinuation of elective surgery during OR construction. The other seven epidemics were associated with perioperative care and caused by gram-negative bacteria. There were six epidemics of primary bacteremia, four of them associated with arterial pressure transducers. Another bacteremia epidemic was caused by the infusion of contaminated commercially prepared normal serum albumin. The remaining primary bacteremia epidemic was caused by using syringes contaminated by ice to obtain blood samples for blood gas determinations. One epidemic of Salmonella gastroenteritis and secondary bacteremia was traced to a contaminated intermittent-suction machine used for postoperative care. Control measures for these epidemics included judicious use and proper decontamination and sterilization of the transducers, recall of the contaminated product, aseptic procedures for caring for arterial cannulae, and proper decontamination of suction equipment. Suggestions for the evaluation and control of potential epidemics are based on the results of these investigations.