The role of the microbiology laboratory in surveillance and control of nosocomial infections.

The microbiology laboratory's rapid and consistent identification of nosocomial pathogens is a keystone in the surveillance and control of hospital-acquired infections. In addition, the laboratory serves as a source of expert consultation for clinicians and infection control personnel and as an "early warning center" for infection problems. In making its contributions to infection control most effective, the laboratory must recognize its capabilities and limitations, must insure that the materials and methods it uses and the specimens it processes meet high standards, must provide retrievable records, and must have a good working knowledge of microbiologic technics used to evaluate both endemic and epidemic infections. Moreover, because laboratory workers come into contact daily with potentially infectious specimens and isolates, the laboratory's contributions to infection control should also include the prevention and surveillance of laboratory-acquired infections.     

Role of the microbiology laboratory in the diagnosis of opportunistic infections in persons infected with human immunodeficiency virus

Patients with defects in the immune system caused by infection with human immunodeficiency virus are predisposed to a variety of opportunistic infections, many of which can be diagnosed by conventional or special microbiological procedures. This article reviews the laboratory diagnosis of bloodstream, lower respiratory tract, gastrointestinal tract, and central nervous system infections in persons infected with human immunodeficiency virus. Laboratories serving health care facilities in which a large number of patients with human immunodeficiency virus infection are cared for should consider enhancing the detection of the specific pathogens affecting these patients by the use of special procedures, including blood culture methods for mycobacteria and fungi, examination of induced sputum for Pneumocystis carinii, and modified acid-fast stains on feces to identify Cryptosporidium and Isospora belli.     

Role of culture and toxin detection in laboratory testing for diagnosis ofClostridium difficile-associated diarrhea

Two variations of an egg yolk agar base medium containing cycloserine, cefoxitin, and fructose (CCFA), one with 250 g and the other with 500 g of cycloserine/ml of agar medium were compared to study the effect of the cycloserine concentration on recovery ofClostridium difficile from stool samples. In addition, the role of prior anaerobic reduction of these media in the detection ofClostridium difficile-associated diarrhea (CDAD) was tested. Each medium was studied over a two-month period, with outcome compared between the testing periods and to historical data from our institution. Clinical correlation of test results was performed. The use of the originally described formulation of CCFA with 500 g of cycloserine/ml of agar combined with 4 h of anaerobic reduction prior to specimen inoculation increased the rate of isolation of toxigenicClostridium difficile from clinical specimens from 6 to 17% (p < 0.001). Combining direct detection of stool toxin and properly performed culture for toxigenicClostridium difficile enhances the potential for diagnosis of CDAD. For optimal performance the culture medium should contain the originally proposed cycloserine concentration of 500 g/ml of agar and should be anaerobically reduced at least 4 h prior to specimen inoculation.     

An overview of nosocomial infections, including the role of the microbiology laboratory.

An estimated 2 million patients develop nosocomial infections in the United States annually. The increasing number of antimicrobial agent-resistant pathogens and high-risk patients in hospitals are challenges to progress in preventing and controlling these infections. While Escherichia coli and Staphylococcus aureus remain the most common pathogens isolated overall from nosocomial infections, coagulase-negative staphylococci (CoNS), organisms previously considered contaminants in most cultures, are now the predominant pathogens in bloodstream infections. The growing number of antimicrobial agent-resistant organisms is troublesome, particularly vancomycin-resistant CoNS and Enterococcus spp. and Pseudomonas aeruginosa resistant to imipenem. The active involvement and cooperation of the microbiology laboratory are important to the infection control program, particularly in surveillance and the use of laboratory services for epidemiologic purposes. Surveillance is used to identify possible infection problems, monitor infection trends, and assess the quality of care in the hospital. It requires high-quality laboratory data that are timely and easily accessible.     

Pediatric nosocomial diarrhea

Nosocomial diarrhea are an important cause of childhood morbidity and mortality. Rotavirus has been recognized as the most important cause of nosocomial gastroenteritidis particularly in infants during winter months. Nosocomial diarrhea are also, caused by bacterial pathogen like Clostridium difficile, Salmonella, Shigella, Campylobacter. Clostridium difficile toxin assay should be considered for patients who are receiving antibiotics. Modifications of hygiene procedures and preventive measures are necessary in order to reduce nosocomial infection.     

Role of the laboratory in diagnosis of organic acidurias

Clinical signs and symptoms of organic acidurias are usually subtle and non-specific. Laboratory evaluation, therefore, is usually the only conclusive way to reach a definitive diagnosis. Defects of amino acid catabolism generally caused by diminished activity or complete absence of specific enzymes usually occurs at the later stages of a pathway and results in organic aciduria. Most of these acids are effectively cleared from the blood by the kidneys, resulting in their concentration in urine to exceed greatly that in serum. Therefore, the detection of increased organic acids is greatly facilitated by a urine assay. The use of dual capillary column gas chromatography should allow the unambiguous determination of all known organic aciduria. Using this method provides a cost-effective alternative to gas chromatography-mass spectrometry.     

An audit of microbiology laboratory utilization: the diagnosis of infection in orthopedic surgery

Objective: To analyse the quality of ordering, collection and transport of specimens for microbiological analysis by a department of orthopedic surgery.
Methods: The analysis consisted of a prospective formal evaluation performed by two consultant microbiologists.
Results: One hundred and seventeen consecutive requests were audited. These requests belonged to 55 clinical episodes, 39 of which were of (presumed) infection and 16 of surveillance. The main sites sampled were: joint 28 (51%), and extra-articular bone or tissue 6 (11%). Of 98 surgical specimens, 20 (20%) yielded a relevant microorganism. The requests were classified as definitely appropriate in 67% and 85% of episodes, by the two consultants respectively. No request was considered unjustified. Collection, handling and transport were categorized as definitely appropriate in 56% and 73% of requests. Analysis of compliance with an existing protocol for prosthetic joint revision revealed similar errors.
Conclusion: Audits of this type can give invaluable information about the area of uncertainty between the clinician and the laboratory and can identify appropriate measures for corrective action.     

Advantages and limits of the surveillance of nosocomial infections from the microbiology laboratory: experience of Meaux hospital

To estimate the incidence of nosocomial infections (NI) in our hospital and to increase healthcare professionals' awareness of hygiene, a prospective study was performed between January and December 2002 from the microbiology laboratory data. On 1334 suspicions of NI, corresponding to 1062 patients, sent to the hygiene correspondents in each medical care unit, the infection control team received 853 answers (64% of sendings) with 430 NI validated. The incidence rate of NI validated was 1.7 NI/1000 days of hospitalisation and 1.6 NI/100 inpatients. The NI were predominantly related to urinary tract (47%), bloodstream (14%), and lower respiratory tract (12%). Transmission of these informations to medical information department permitted a valorisation of additional 16,000 ISA points. This prospective study permitted to develop a network of hygiene correspondents in every medical care units. None of the medical care units was unharmed by NI but the exhaustive declaration of NI seems difficult to realise. This study permitted to point out some dysfunctionments in the management of invasive procedures and to improve these practices.     

Competency assessment in the clinical microbiology laboratory

The laboratory comprises an invaluable part of the total health care provided to patients. Competency assessment is one method by which we can verify that our employees are competent to perform laboratory testing and report accurate and timely results. To derive the greatest benefit from the inclusion of competency assessment in the laboratory, we must be sure that we are addressing areas where our efforts can be best utilized to optimize patient care. To be competent, an employee must know how to perform a test, must have the ability to perform the test, must be able to perform the test properly without supervision, and know when there is a problem with the test that must be solved. In some cases, competency assessment protocols may demonstrate areas of competence but can fail to disclose incompetence. For example, challenges of low-complexity tasks (such as reading the technical procedure manual) are inferior to challenges that measure understanding and execution of a protocol, and poorly designed competency challenges will probably not detect substandard laboratory performance. Thus, if we are to receive the greatest benefit from our competency assessment programs, which may be time-consuming for the supervisors and the staff as well, we must not only meet the letter of the law but also find a way to make these assessments meaningful, instructive, and able to detect areas of concern. As we address competency assessment in our laboratories, we must understand that when done properly, competency assessment will reward our organizations and assist us in providing the best possible care to our patients.     

Comparison of four laboratory tests for diagnosis ofClostridium difficile-associated diarrhea

Four different laboratory tests for diagnosis ofClostridium difficile-associated diarrhea were compared to determine the optimal one for management of patients with hospital-acquired diarrhea. Stool samples from 231 patients with diarrhea were tested by the following methods: culture forClostridium difficile with subsequent determination of exotoxin production, with a toxigenicClostridium difficile positive (TCP) result considered truly positive; enzyme immunoassay (EIA); latex agglutination test; and an immunobinding blot assay. The rates of positive results were as follows: EIA 5.5%, TCP 7.3%, latex agglutination 16.7%, and immunobinding blot assay 26.1%. Compared to the TCP results, the sensitivity and specificity were, respectively, 61 and 98% for EIA, 47 and 85% for latex agglutination, and 60 and 76% for the immunobinding blot assay. Samples from patients with 6 stools/day were TCP and EIA positive in 27 and 17% of cases, respectively, whereas in patients with < 6 stools/day, these percentages decreased to 2 and 3%, respectively (p < 0.001). In hospitalized patients with 6 stools/day, EIA appears to be the optimal test for diagnosis ofClostridium difficile-associated diarrhea, with a 73% positive predictive value and a 97% negative predictive value. However, in patients with < 6 stools/day, the prevalence ofClostridium difficile is low, and laboratory detection of this organism remains problematic.