Smallpox: gone but not forgotten.

Smallpox represents both the acme of man's efforts to combat infectious diseases and one of his greatest fears. The disease emerged in prehistoric times to spread throughout the world causing blindness and death in millions of people. An acute infection caused by variola virus, one of the Orthopoxviruses, with skin eruption and marked toxemia had an average case fatality rate of 30%. Variola minor, a milder form of the disease, had a case fatality of one percent. Humans are the sole host, and survival confers lifelong immunity. Immunization was practiced since ancient times by inoculation with the variola virus until Jenner's demonstration of the efficacy and safety of vaccination with vaccinia virus. Following an intensive eradication effort by the World Health Organization, the world was declared to be free of smallpox in 1979. The decision to destroy all remaining stocks of variola virus in 1999 has met with some controversy.

Role of the microbiology laboratory in care of the immunosuppressed patient.

In the immunosuppressed patient the usual hallmarks of infection, such as leukocytosis and antibody response, may be absent; thus the microbiology laboratory plays a fundamental role in the diagnosis of infection. Methods used to demonstrate microorganisms in a specimen submitted to the laboratory include visualization techniques, culture, and non-cultural methods involving immunologic, immunochemical, and nucleic acid probe methodologies. Because infections in the immunosuppressed patient may be caused by unusual organisms whose identification requires special techniques, close communication between the physician and the laboratory is important. New technologies allow the clinical microbiology laboratory to gather important diagnostic information more readily. When these results are delivered rapidly to physicians via computerized information systems, care of the immunosuppressed patient is significantly enhanced.

Sero group C streptococcal infection in intravenous drug abusers: a report of two cases.

Two cases of group C streptococcal bacteremia in intravenous drug abusers are described. Both patients had joint involvement and may have been immunocompromised. The literature pertinent to this organism is briefly reviewed.

Rapid detection and identification of pathogenic mycobacteria by combining radiometric and nucleic acid probe methods.

The combination of radiometric methodology (BACTEC 12B) and probe technology for recovery and identification of mycobacteria was studied in two large hospital laboratories. The sediment from vials with positive growth indices was tested with DNA probes specific for Mycobacterium tuberculosis, Mycobacterium avium, and Mycobacterium intracellulare. The sensitivity of the radiometric method and the specificity of the probes resulted in a marked reduction in the time to the final report. Biochemical testing could be eliminated on isolates giving a positive reaction with one of the probes. Some 176 isolates of M. tuberculosis, 110 of M. avium, and 5 of M. intracellulare were recovered. Two-thirds of these isolates were detected and identified within 2 weeks of inoculation and the remainder was detected by 4 weeks, a reduction of 5 to 7 weeks to the final report.

Evaluation of substrates for radiometric detection of bacteria in blood cultures.

Various 14C-labeled substrates were evaluated for their potential use in blood culture media. These uniformly labeled compounds were added to hypertonic and anaerobic formulations of modified Columbia broth and compared with analogous BACTEC media with the BACTEC 460. Different bacterial species gave significant growth indices when 2.0 microCi of labeled glucose, glutamic acid, aspartic acid, arginine, or formate was used alone or in combinations in the experimental media. The combination of glucose, glutamic acid, and sodium formate was selected, and simulated blood cultures with representative aerobic, facultative, and anaerobic bacteria and a yeast were compared with BACTEC vials. Under these conditions, the experimental media often became positive several hours earlier than the BACTEC vials and usually produced higher growth indices.

Diagnostic laboratory procedures in infectious diseases.

Useful diagnostic information can be provided by the microbiology laboratory in a variety of infectious diseases. It is important to obtain an appropriate specimen and to provide the laboratory with relevant information. The value and limitations of in vitro susceptibility testing are discussed.

Epidemiologic factors affecting antimicrobial resistance of common bacterial isolates.

The pattern of antimicrobial resistance of common bacterial isolates obtained from various groups of patients at a large tertiary-care center was compared with the pattern of resistance seen at a primary-care community hospital. At the tertiary-care center, significant differences in susceptibility were seen between pediatric and adult groups. In the tertiary-care center, the inpatients were more likely than the outpatients to have resistant staphylococcal and enterobacterial strains. Comparison of the overall resistance at the tertiary-care center and the primary-care hospital showed that resistance to cephalosporins, piperacillin, and aminoglycosides was significantly higher at the tertiary-care hospital than at the community hospital. Striking differences were noted in the resistance of nosocomial Enterobacter and Citrobacter isolates. Hospitals should be cautious in extrapolating nationwide data to their particular institutions.

Preliminary evaluation of a rapid colorimetric method for identification of pathogenic Neisseria.

A rapid colorimetric method for the identification of pathogenic Neisseria (Identicult-Neisseria; Scott Laboratories, Inc.) based on beta-galactosidase, gamma-glutamylaminopeptidase, and gamma-prolylaminopeptidase is described. All 82 clinical isolates of Neisseria gonorrhoeae, 9 clinical isolates of N. meningitidis, and 5 clinical isolates of N. lactamica were correctly determined to the species level, as were 4 isolates of Branhamella catarrhalis. Reactions were prompt and easily interpreted. The system should be extremely useful in clinical laboratories.

Preliminary evaluation of a rapid colorimetric method for the presumptive identification of group A streptococci and enterococci.

A rapid colorimetric method for the presumptive identification of group A streptococci and enterococci based upon pyroglutamyl aminopeptidase activity is described. Of 76 group A streptococcal isolates from primary plates, 83 gave positive reactions, and the remaining 7 were positive on retesting in pure culture. Of the 31 enterococcal isolates tested, all gave positive reactions. Despite occasional positive reactions with staphylococci and Klebsiella pneumoniae, the test could be useful and cost-effective in the clinical laboratory.

Comparison of the PRAS II, AN-Ident, and RapID-ANA systems for identification of anaerobic bacteria.

Two rapid systems for the identification of anaerobes were compared to a conventional growth system aided by a computer. The rapid systems (AN-Ident and RapID-ANA) are non-growth-dependent micromethods that identify anaerobes in 4 h by the action of various constitutive enzymes on chromogenic substrates. The organisms tested were 98 anaerobes, most of which were clinical isolates. The AN-Ident system identified 76 of these to species level and 86 to genus level; the RapID-ANA system correctly identified 74 of the organisms to species level and identified 93 to genus level. The PRAS II system correctly identified 77 to species level and 96 to genus level. In most instances, adequate identification could be obtained with either of the two rapid systems, but the conventional PRAS II system remains the most accurate.

Evaluation of a microtiter system for identification of anaerobic bacteria.

The Anaerobe Combo Panel (American MicroScan, Mahwah, N.J.) was evaluated for its ability to identify anaerobic bacteria. The frozen, 96-well panel utilizes 24 biochemical reactions and four antimicrobial agents for species identification. The Anaerobe Combo Panel was used to test 114 clinical isolates of strict anaerobes. Reactions were read after 48 h, and the results were compared with those obtained with the PRAS II system (Scott Laboratories, Inc., Fiskeville, R.I.). Discrepancies between the two systems were resolved by gas-liquid chromatography. With the Anaerobe Combo Panel, 84% of the organisms were able to grow, and 89% of these were correctly identified to genus level and 78% to species level. The Anaerobe Combo Panel was easy to inoculate and read, but some of the reactions were difficult to interpret, and not all of the derived codes were found in the code book.

Evaluation of the Bacteriuria Detection Device.

The ability of the Bacteriuria Detection Device (BDD) (Marion Laboratories, Kansas City, Mo.) to detect significant bacteriuria was evaluated. Quantitative plating and BDD results were compared for 513 clinical specimens, 188 of which were voided. Eighty-seven specimens (17%) could not be tested because of clogging or excessive pigmentation. Specimens were considered positive if they contained more than 10(4) bacteria per ml. Thirteen specimens gave false-negative BDD results; 10 of these contained gram-positive cocci. The sensitivity of the BDD test was calculated to be 89%; the specificity, 65%. The predictive value of a negative test was 94%; that of a positive test was 49%. The efficiency of the BDD test was 71.6%. The BDD has the potential for providing rapid detection of bacteriuria, but requires further improvement before it can reliably be substituted for urine culture.

Evaluation of slide agglutination methods for identifying group D streptococci.

Three commercial reagents for the rapid identification of group D streptococci by slide agglutination were evaluated. These included SeroSTAT (Scott Laboratories, Fiskeville, R.I.), Streptex (Wellcome Laboratories, Research Triangle Park, N.C.), and Phadebact (Pharmacia Diagnostics, Piscataway, N.J.). The methods included direct colony testing, enzyme extraction with pronase, and broth culture. A total of 72 strains of group D streptococci were tested. The SeroSTAT and Streptex reagents with pronase extraction each identified 65 (90%) of the strains. The SeroSTAT reagent was somewhat more specific since it did not cross-react with other streptococci of the viridans group. The Phadebact reagent was nonreactive. We conclude that the latex reagents can be very useful for the quick recognition of group D streptococci in the clinical laboratory.

Speciation of coagulase-negative staphylococci in the clinical laboratory.

The purpose of this study was to evaluate the efficacy of the API Staph System for the speciation of coagulase-negative staphylococci. Three hundred and seventy-one coagulase-negative clinical isolates were studied; 50% of these could be speciated using the code profiles of the API System. By reference to the Kloos and Schleifer schema, 93% of the isolates could be speciated. The distribution of the various staphylococcal species in clinical specimens was determined. It was concluded that the API Staph System would be a satisfactory method of speciation if the data base could be expanded. Such speciation may at times be helpful in interpreting the significance of coagulase-negative staphylococcal isolates in the clinical laboratory.