Investigation of suspected laboratory cross-contamination: interpretation of single smear-negative, positive cultures for Mycobacterium tuberculosis

Restriction fragment length polymorphism (RFLP) analysis can be used to assess genetic relatedness of Mycobacterium tuberculosis isolates. This study reports a collaborative investigation of false-positive cultures for M. tuberculosis, suspected when the DNA fingerprint from an index case matched an epidemiologically improbable source case. RFLP analysis matched fingerprints in ten of 16 cases of suspected laboratory contamination to four separate smear-positive sources that were processed on the same day in the same laboratory. All single smear-negative, positive cultures processed on the same day as smear-positive specimens should be reviewed on a case-by-case basis to identify possible false-positive cultures.

Emergence of an invasive clone of nontoxigenic Corynebacterium diphtheriae in the urban poor population of Vancouver, Canada

Invasive disease due to Corynebacterium diphtheriae is rare in North America. Here we describe the emergence of a predominant clone of a nontoxigenic strain of C. diphtheriae in the impoverished population of Vancouver's downtown core. This clone has caused significant morbidity and contributed to at least two deaths. Over a 5-year period, seven cases of bacteremia due to C. diphtheriae were detected in patients admitted to Vancouver hospitals. Injection drug use, diabetes mellitus, skin colonization/infection with C. diphtheriae, and homelessness all appeared to be related to the development of bacteremia with the organism. Ribotyping of isolates recovered from blood culture revealed a predominant ribotype pattern that has not previously been reported in North America.

Agrobacterium yellow group: bacteremia and possible septic arthritis following peripheral blood stem cell transplantation

A 47-year-old male patient developed sepsis and monoarticular arthritis following autologous stem cell transplantation for recurrent Hodgkin's disease. Blood cultures were positive for Agrobacterium yellow group. The knee pain and swelling responded promptly to the institution of empirical broad-spectrum antibiotics. Recurrent bacteremia developed necessitating Hickman line removal for eventual resolution of the infection. Transplant physicians should be aware of this unusual pathogen and the potential for both persistent line-related sepsis and possible septic arthritis.

The toilet as a transmission vector of vancomycin-resistant enterococci

An elderly woman, admitted to the intensive care unit of a large university teaching hospital, was found to be colonized with vancomycin-resistant enterococci leading to the temporary closure of the unit. She had acquired the organism nosocomially, most likely from an environmental source, which had been contaminated when the toilet of a former patient, also colonized with vancomycin-resistant enterococci, had become blocked and overflowed throughout his and the adjoining room. This is the first report of a hospital toilet as the transmission vector for vancomycin-resistant enterococci.

Psoriatic plaques exhibit red autofluorescence that is due to protoporphyrin IX

In evaluating the autofluorescence properties of normal and diseased skin we discovered that psoriatic plaques can emit a distinct red fluorescence when illuminated with UVA or blue light. Using a macrospectrofluorometer equipped with a 442 nm excitation laser, a sharp in vivo fluorescence emission peak around 635 nm could be demonstrated within the plaques of 34 of 75 (45%) patients with psoriasis. This peak was absent from normal appearing skin of psoriatic patients and also from the skin of 66 patients with other dermatologic diseases. A microspectrofluorometer coupled with the same excitation laser was used to obtain emission spectra of separated epidermal sheets and dermis from plaques demonstrating macroscopic red autofluorescence. An emission peak around 635 nm was observed in all three patients thus studied, but only on spectra obtained from the epidermis. Additional spectra of vertical microscopic sections of intact psoriatic skin from five other patients revealed that the peak originated from the stratum corneum. Emission spectra from other microlocations including the mid-epidermis and dermis of psoriatic and normal skin, as well as the stratum corneum of normal skin, failed to demonstrate a 635 nm peak. The excitation and emission fluorescence spectra of acid extracts of psoriatic scale from five patients were all similar to those of protoporphyrin IX in acid solution. High performance liquid chromatography identified the presence of protoporphyrin IX in the acid extracts from psoriatic scale of the same patients. We conclude that native psoriatic plaques can exhibit red autofluorescence that is due to elevated levels of protoporphyrin IX within scales.

Contemporary context for early-onset group B streptococcal sepsis of the newborn

We examined early-onset newborn group B streptococcal (GBS) infection among the population of a large obstetric center in western Canada for the contemporary period 1987 to 1992. Attack rates for "definite" (bacteremic) and "presumptive" (urine group B antigen positive with clinical evidence) GBS infections were 0.85 and 0.90 per 1000. Ten GBS-associated stillbirths were recorded. Seven deaths occurred among bacteremic newborns (18.4%). Using definitions of Boyer and Gotoff, 87.2% of all mothers with infected newborns manifested at least one risk factor, and 69.8% of all febrile pregnancies with either definition of infected newborn and 61.9% of a subset of the same with bacteremic offspring had maternal temperature 38 degrees C or higher prior to delivery. For our population, recommendations for universal antepartum GBS screening and intrapartum prophylaxis must be discussed in the context of an existing low frequency of bacteremic disease and with the understanding that fever in pregnancy may be enough to warrant greater intervention that might further reduce the rate of infection.

The utility of latex agglutination assays in the diagnosis of pediatric viral gastroenteritis

To design a rapid and efficient protocol for processing pediatric stool specimens, the authors used 434 specimens to evaluate two commercial latex assays to detect rotavirus (Meritec-Rotavirus and Rotalex) and one to detect adenovirus (Adenolex). Rotavirus latex assay results were compared with electron microscopic examination and adenovirus latex assay results with virus culture. Ninety-two specimens (21%) were positive for rotavirus and 28 (6.5%) for adenovirus; 5 (1%) had both viruses. The sensitivity, specificity, positive predictive values, and negative predictive values for the three assays were, respectively, as follows: Meritec-Rotavirus (97%, 99%, 97%, 99%), Rotalex (91%, 99%, 94%, 98%), and Adenolex (46%, 99%, 77%, 97%). For primary rotavirus screening, the Meritec-Rotavirus and Rotalex latex assays offer a good alternative to electron microscopic examination. For primary adenovirus screening, the low sensitivity of the Adenolex latex assay precludes its use as a routine screen. Its excellent specificity, however, makes it a useful tool for culture confirmation.

Antimicrobial susceptibilities and beta-lactamase characterization of Capnocytophaga species

Capnocytophaga species have been associated with a wide variety of infections in both immunocompetent and immunocompromised patients. On the basis of data from antimicrobial susceptibility studies, beta-lactam antibiotics have been considered efficacious therapy. Six of 19 isolates from primarily clinical sources across Canada demonstrated beta-lactamase production, and agar dilution susceptibility testing showed broad resistance to beta-lactam antibiotics. For the beta-lactamase producing isolates, clavulanate reduced the MIC of amoxicillin for 90% of the strains tested by 64-fold. Isolates were highly susceptible to clindamycin, imipenem, and ciprofloxacin. Characterization of the beta-lactamases produced by two of these isolates (Van1 and Van2) was performed. Isoelectric focusing revealed an identical isoelectric point of 5.6 for both enzymes, but they had markedly different relative hydrolysis efficiencies, and different conditions were required to extract the enzymes. This study demonstrates the production of different types of beta-lactamases by Capnocytophaga spp. and suggests the need to screen all clinical isolates of Capnocytophaga spp. for the presence of beta-lactamases.

Hepatitis & HIV: prevalence of infection and changing attitudes toward infection control procedures in British Columbia

Dental professionals attending the annual meeting of the College of Dental Surgeons of British Columbia in June 1990 were involved in a survey to assess the prevalence of infection with Hepatitis B, Hepatitis C and Human Immunodeficiency viruses, the acceptance of vaccination for protection against Hepatitis B virus, and the compliance with infection control guidelines. Participation was voluntary and anonymous and required completion of a questionnaire and donation of a blood sample. Four hundred one of 1,995 convention attendees participated. Fourteen were found to have markers of Hepatitis B infection; 13 had antibodies to both Hepatitis B surface antigen and Hepatitis B core antigen, and one was positive for Hepatitis B surface antigen. One individual had markers for both Hepatitis C and Hepatitis B viruses. None tested positive for antibody to Human Immunodeficiency virus. Vaccination against Hepatitis B virus was reported overall by 67 percent of the participants, but dentists and hygienists had a higher rate of vaccination (82 percent and 81 percent, respectively) when compared to dental assistants (41 percent; P less than .001). Acceptance of infection control procedures was high, with 92 percent of participants reporting use of gloves for all patients and 82 percent reporting use of masks and eye protection.

Normal flora and mucosal immunity of the head and neck

The study of the human resident flora has grown from Antony van Leeuwenhoek's simple descriptions some 300 years ago to the sophisticated investigations being done today. The acquisition of organisms and the subsequent course of either stable colonization or invasion of the host involve complex host-parasite interactions. From one perspective, clearly host factors are operative that appear to select against certain species while being permissive for others. From another perspective, microbial species that are successful at colonization must overcome certain host factors to maintain a selective advantage and flourish within a particular body habitat. It is intriguing that whereas host mucosal defenses are a significant influence contributing to selection of the resident flora, it is this established flora that provides the host with perhaps its most important local defense system. In the head and neck areas, many of these mucosal surfaces are contiguous and thus for the most part share a common resident flora. These organisms are rarely involved in infection unless some breach of the mucosal surface or some upset in the balance of the normal flora occurs. On these occasions, the host is susceptible to infection from both newly acquired organisms and those previously present, which may now become invasive. In any event, it is clear that improved knowledge of the normal flora of the head and neck is essential for understanding and for effective treatment of infectious processes in this area. It is hoped that a better appreciation of the important role of the normal flora in maintaining the host mucosal defenses will further focus our attention on its preservation.