September 1999
SAN FRANCISCO - Measures must be instituted to prevent nosocomial infections in the pediatric intensive care unit (PICU). In a recent report from the National Nosocomial Infections Surveillance (NNIS) system of the Centers for Disease Control and Prevention (CDC), the PICU ranks third after the burn ICU and high-risk nursery (babies weighing <1,000 grams) for the rate of central line-associated bloodstream infections (BSIs).
"There are many unanswered questions regarding prevention of nosocomial infections and antimicrobial resistance in the PICUs, and there is a need for studies to be performed to answer some of those questions," said Jane D. Siegel, MD, professor, department of pediatrics, University of Texas Southwestern Medical Center, Dallas.
The CDC and the National Association for Children's Hospitals and Related Institutions (NACHRI) have entered into a cooperative agreement to create a network of pediatric health care facilities in which nosocomial infection and antimicrobial resistance can be studied, she said at the Ninth Annual Meeting of the Society for Healthcare Epidemiology of America here.
"The objective is to get a baseline of where we are now and then to design and evaluate preventive interventions." Thus far, said Siegel, 48 hospitals are participating with a total of 875 PICU beds.
"From our baseline inventory survey, we can see that our median rates for BSIs, ventilator-associated pneumonia, and urinary tract infections (UTIs) in the PICU are similar to the rates reported to NNIS but with wider variation," she said.
Standardization of definitions and surveillance methods will likely decrease the variation among institutions, said Siegel.
Severity of illness cores based on physiologic changes present on admission to the PICU are used by pediatric intensivists to stratify their patient populations and predict the risk of mortality. There has been interest in using these scores to predict the risk of nosocomial infections, said Siegel.
"Although there are two studies, one from Washington National Children's Hospital and the other from Toronto Children's Hospital, that suggest there is a higher risk of nosocomial infection in patients with higher severity of illness scores, I think that the present scoring systems are not ideal for use by hospital epidemiologists because they do not take into account the specific factors or therapeutic interventions that put patients at risk for nosocomial infections," she said.
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In the NNIS report of nosocomial infections in the PICU for 1992-1997 that was published recently in Pediatrics,coagulase-negative Staphylococcus aureusaccounts for almost 40% of BSIs, which is dramatically greater than other organisms, said Siegel. This raises the question of whether contaminants have been distinguished from true pathogens, she said.
"This is a challenge for us that we need to focus on because I suspect that a fair amount of vancomycin is being used to treat coagulase-negative staphylococci that are actually contaminants. We could perform an important service if we could figure out ways to sort that out."
After coagulase-negative staphylococci, the most frequently isolated organisms from BSIs were Enterococcus 11.2%),fungi (9.5%), S. aureus(9.3%), Enterobacter sp. (6.2%) and Pseudomonassp. (4.9%). Nearly 50% of the fungal isolates are Candidaalbicans the other 50% are a variety of species that are problematic because of increased resistance to antifungal agents.
Many of the risk factors for selection of resistant organisms in the PICU are similar to those described for adult populations.
Investigators from Washington National Children's Hospital looked for colonization with resistant gram-negatives by culturing patients on a daily basis from the day of admission to the PICU. Of the 20% who were colonized with resistant organisms, 50% were colonized within the first three days of their PICU stay, suggesting acquisition from the community prior to their PICU admission.
Researchers gave each patient's family a questionnaire to complete to look at a variety of potential risk factors.
"The risk factor most strongly predictive of colonization with resistant gram-negative organisms in the first three PICU days was coming from a chronic care facility," said Siegel of the study questionnaire findings. Other independent predictors of pre-existing colonization were treatment with intravenous antibiotics in the preceding 12 months, household contacts who were hospitalized during the preceding 12 months and the number of previous ICU admissions.
"This does point out that we need to be looking for risk factors in patients admitted to the PICU, perform surveillance cultures and consider putting such high-risk patients on contact precautions until we know that they are not colonized with resistant organisms."
Should everyone who comes to the ICU be cultured? she asked. "No. I think that certainly patients coming from chronic care facilities or other acute care hospitals would be candidates for targeted surveillance cultures."
The availability of viral diagnostic techniques is absolutely critical in recognizing viruses as the cause of nosocomial infections, said Siegel. A study from Children's Hospital in Buffalo published in 1984 identified viruses as the second most frequent cause of nosocomial infections in the hospital overall, she said. Other studies indicate that viruses are less of a problem in the PICU compared with other units within the hospital.
There have been several reports of respiratory syncytial virus (RSV) spread in units with high mortality rates. "I do think we are doing better with our prevention of nosocomial transmission of both RSV and rotavirus as we understand more about the modes of transmission and the precautions (contact) that are effective to prevent spread," she said.
"We hope that selected use of the RSV monoclonal antibody in high-risk patients and the universal use of rotavirus vaccine will decrease the number of cases overall and therefore reduce the opportunities for exposure within the hospital."
Other measures to reduce the risk of nosocomial viral infection include the use of private rooms, cohorting patients with the same infectious agent, cohorting staff, effective visitor screening, health care immunization and the use of needleless devices for prevention of exposure to bloodborne pathogens.
Visitor screening is especially important for prevention of nosocomial viral infection, said Siegel. "We know that a number of our nosocomial viral infections, even in the PICU, are acquired from visitors, young siblings or adults who come in with a viral infection."
Patients and health care workers should be immunized against vaccine-preventable diseases, especially varicella and influenza, for prevention of nosocomial transmission of these agents to high-risk patients. Standard precautions are effective to prevent transmission of Cytomegalovirus, she said.
Fungi are the agents most frequently isolated from PICU patients with UTIs (22.7%), Candida albicans being the most common species.
"This is a key point because it is often difficult to distinguish between catheter colonization and true UTI when Candida sp. is isolated from a culture of urine obtained through an indwelling urinary catheter."
It is an extremely important distinction in febrile neutropenic immunosuppressed patients because funguria may be the first indication of serious invasive disease involving organs outside the urinary tract. She also stressed the importance of removing an indwelling catheter and obtaining urine for culture through a newly placed catheter before initiating antifungal therapy.
The most common bacteria causing UTIs in these patients are Escherichia coli 19%), Pseudomonas 13.1%), Enterobacter sp. (10.3%), Enterococcus 10%) and Klebsiella pneumoniae(7.3%).
Measures must also be instituted for prevention of environmental fungal infections in PICU patients, Siegel said. As the number of PICU patients who are immunocompromised increases, so does the risk of invasive aspergillosis and serious disease caused by other environmental fungi.
Therefore, efforts must be made to prevent contamination of the environment with outside air or construction dust that is laden with infectious particles, she said. Ceilings and walls stained from water leaks that are not cleaned within 72 hours are likely to be contaminated with fungal elements as well, said Siegel.
"Some institutions with large transplant populations and experience with aspergillosis cases have chosen to use centrally HEPA-filtered air handlers and positive pressure ventilation to reduce the likelihood of exposure. I am not recommending this for routine use in all PICUs but rather as a consideration when an institution assesses its risk of environmental fungal infections."
For more information
- Siegel J. Emerging controversies in the pediatric intensive care areas. Symposium I. Presented at the Society for Healthcare Epidemiology of America meeting. April 18-20. San Francisco.
- CDC NNIS System. National Nosocomial Infections Surveillance (NNIS) System report, data summary from October 1986-April 1998. Issued June 1998. Am J Infect Control 1998;26:522-33.
- Richards MJ, Edwards JR, Culver DH, et al. Nosocomial infections in pediatric intensive care unites in the United States. Pediatrics.1999;103(4):e39.
- Jarvis WR, Robles B. Nosocomial infections in pediatric patients. Adv Pediatr Infect Dis.1997;12:243-95.
- Toltzis P, Hoyen C, Spinner-Block S, et al. Factors that predict pre-existing colonization with antibiotic-resistant gram-negative bacilli in patients admitted to a pediatric intensive care unit. Pediatrics. 999;103:719-23.
- Singh-Naz N, Sprague BM, Patel KM, et al. Risk factors for nosocomial infection in critically ill children: A prospective study. Crit Care Med. 1996;24:875-8.
- Archibald LK, Manning M, Bell LB, et al. Patient density, nurse-to-patient ratio and nosocomial infection risk in a pediatric cardiac intensive care unit. Pediatr Infect Dis J 1997;16:1045-8.
- Pollock E, Ford-Jones L, Corey M, et al. Use of the Pediatric Risk of Mortality score to predict nosocomial infection in a pediatric intensive care unit. Crit Care Med 1991;19:160.
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