False positive EBNA IgM and IgG antibody tests for infectious mononucleosis in children.

OBJECTIVES: To assess the reliability of the Monolert test, a new enzyme-linked immunosorbent assay for the diagnosis of acute infectious mononucleosis (IM). DESIGN: A retrospective laboratory and clinical analysis of 38 children diagnosed with acute IM. SETTING: A suburban pediatric practice in Connecticut. PATIENTS: Thirty-eight children (ages 18 months to 17 years) who were diagnosed with acute IM using the Monolert test during the period October 1992 to August 1993. RESULTS: Eighty-three percent of these children had no evidence of Epstein-Barr virus infection on subsequent investigation. The false positive results of the Monolert test could not be explained on the basis of elevated antibody titers to either cytomegalovirus or Borrelia burgdorferi. CONCLUSION: Monolert is a poor screening test and is of little apparent value as a diagnostic test for acute Epstein-Barr virus infection in pediatric patients.

Seroprevalence of antibodies to hepatitis C virus in high-risk hospital personnel.

OBJECTIVE: To estimate seroprevalence of antibodies to hepatitis C virus in healthcare workers at high risk for blood exposure. DESIGN: A prospective anonymous seroprevalence survey of 243 healthcare workers. SETTING: A large referral hospital and 2 community hospitals in Connecticut. PARTICIPANTS: Healthcare workers, including surgical personnel, dentists, hemodialysis workers, laboratory workers, and emergency room staff. RESULTS: Antibody to hepatitis C virus was found in 1.6% (95% confidence interval [CI95] = 0-3.2%) of healthcare workers. None of the prevalent seropositives had a past history of clinical hepatitis or blood transfusion. CONCLUSIONS: We conclude that the seroprevalence of hepatitis C virus in healthcare workers with a high degree of blood exposure is low and is similar to seroprevalence rates reported for volunteer blood donors. However, first-generation hepatitis C serologic tests may underestimate the true prevalence of infection. Further studies, including prospective cohort studies, will be required to determine if the low seroprevalence is from low risk of acquisition of disease or from loss of measurable humoral antibody response to the virus.

Susceptibilities of Pseudomonas species to tetracycline, minocycline, gentamicin, and tobramycin.

Members of the genus Pseudomonas are widely implicated in human disease. Although most isolates are P. aeruginosa, there have been serious outbreaks of infection with other members of the genus. The susceptibility patterns of 5) Pseudomonas isolates are reported. It was notable that of the four antibiotics tested, uniform susceptibility was observed with minocycline.

The microdilution antibiotic susceptibility test. Bacteroides fragilis.

A micro broth-dilution method was developed for the antibiotic susceptibility testing of Bacteroides frgilis. Eighty strains of B. fragilis were tested against six antibiotics using the agar dilution test as the reference method. The microdilution test yielded results in 24 hours, and agreement with the reference test was satisfactory. Certain subspecies-specific patterns of antibiotic susceptibility were observed. However, larger numbers of subspecies should be evaluated before subspeciation of B. fragilis can be used as a reliable predictor of antibiotic susceptibility.

An assessment of available rapid immunologic diagnostic methods.

A critical evaluation of immunologic methods for diagnosis is presented. The issues of antibody versus antigen detection are addressed. Reverse capture immunoglobulin M detection is described as a potentially useful method. Agglutination procedures currently in use for antigen detection are summarized. Comparative evaluations of commercially available products are presented. The final issue discussed is that of enzyme immunoassay versus fluorescent antibody microscopy. Using Chlamydia detection as an example, advantages and disadvantages of each technology are assessed.

Clinical and ecological characteristics of Vibrio vulnificus in the northeastern United States.

Multiple seawater sites in the northeastern United States, particularly Long Island Sound, and shellfish from Long Island Sound were sampled from April to November for 3 successive yr, 1983-1985. Hospitals in coastal and metropolitan areas of Connecticut were surveyed for the same 3-yr period, Vibrio vulnificus can be found in these waters during the summer months. The appearance of these virulent bacteria in both seawater and shellfish are a function of the water temperature; no V. vulnificus could be isolated until the temperature was approximately 17 degrees C. Although the risk of infection is small, as shown by isolation of this organism from patients, certain high-risk groups exist. Consumption of raw shell fish during the summer months should be discouraged in people with liver disease or patients on immunosuppressive therapy.

Rapid screening of urine for significant bacteriuria by Gram stain, acridine orange stain, and the Autobac MTS system.

Urine specimens submitted for microbiologic examination were screened for evidence of bacteriuria by three rapid methods: Gram staining, acridine orange staining, and the Autobac MTS system. The screening results were compared with those obtained by semiquantitative colony counts on agar plates. In this comparative study 1055 urine specimens were examined, of which 146 (13.8%) had colony counts of greater than or equal to 1 X 10(5)/ml. All three urine screening methods detected this level of bacteriuria at a sensitivity of 98% and a specificity of 55.2% (acridine orange), 66.0% (Gram stain), and 83.2% (Autobac), respectively. Of the 1055 urine specimens examined, 185 (17.5%) had colony counts of greater than or equal to 1 X 10(4)/ml, at which level the sensitivity of the three methods was 93% and the specificity was 56.7% (acridine orange), 68.0% (Gram stain), and 86.0% (Autobac), respectively. For any level of sensitivity, the Autobac urine screen was shown to be more specific than either the Gram stain or the acridine orange method. The acridine orange stain was the least specific urine screen, especially at the upper limits of sensitivity.

Improved immunologic detection of Clostridium difficile antigen by counterimmunoelectrophoresis.

An improved counterimmunoelectrophoresis (CIE) procedure for detection of Clostridium difficile antigen is described. Commercially available antiserum to C. difficile toxin was absorbed with whole cells of C. difficile. CIE (absorbed) was 100% sensitive and 77.5% specific when compared to the tissue culture toxin assay. Instances are noted in which the CIE (absorbed) and/or bacterial culture was positive and the tissue culture assay was negative.

DNA probe versus culture for detection of Mycoplasma pneumoniae in clinical specimens.

The laboratory diagnosis of Mycoplasma pneumoniae is often difficult because of lengthy and complicated cultural methods and serological tests that may be both insensitive and nonspecific. In this study, 82 patients suspected of Mycoplasma pneumonia were cultured for M. pneumoniae, and their respiratory secretions were tested by a DNA probe for M. pneumoniae. The probe test was 100% sensitive and 98% specific compared to culture. This DNA probe, then, is an effective alternative method for the detection of M. pneumoniae in respiratory specimens.

Infective endocarditis due to penicillin-tolerant Streptococcus bovis.

Two Streptococcus bovis isolates obtained from patients with endocarditis were found to be tolerant to penicillin and other cell wall active agents. By time-kill analysis, penicillin and streptomycin acted synergistically against these strains. The existence of tolerant S. bovis strains should be considered when initially choosing antibiotics for the treatment of serious S. bovis infections.

Rapid detection of Chlamydia trachomatis by an enzyme immunoassay method.

Chlamydia trachomatis has been shown to be a major cause of sexually transmitted diseases in the United States. An enzyme immunoassay (Abbot Laboratories) has been developed that detects chlamydial antigen directly in the urogenital specimens of patients. We have evaluated specimens from 1,074 patients belonging to one of three risk groups. Three swabs were collected from each patient--one each for Neisseria gonorrhoeae, chlamydia cell culture, and enzyme immunoassay. When compared with cell culture, the sensitivity and specificity of the enzyme immunoassay for symptomatic males and females attending a sexually transmitted disease clinic was 82% and 100%, and 91.3% and 95.0%, respectively. A moderate risk group, consisting of female patients seen at either urology or gynecology clinics for genitourinary symptoms was also evaluated. The sensitivity and specificity of the test on this group was 96% and 96.7%. A population of females at low risk were also screened for chlamydial infection. In this group, the sensitivity and specificity of the enzyme immunoassay was 89.3% and 93.2%, respectively. This rapid test is a highly specific and sensitive procedure for the detection of chlamydial antigen in genital specimens from high risk female patients as well as symptomatic males.

Role of Chlamydia trachomatis and Mycoplasma pneumoniae in acute pharyngitis in children.

In a group of children with acute, nonstreptococcal pharyngitis, only one (2%) of the 44 children tested showed serologic or direct-immunofluorescence evidence of a recent Chlamydia trachomatis infection. Only two (5%) of the 43 children tested showed serologic evidence of a recent Mycoplasma pneumoniae infection. Neither C. trachomatis nor M. pneumoniae appears to be an important cause of acute pharyngitis in children.

A five-year multicenter study of the susceptibility of the Bacteroides fragilis group isolates to cephalosporins, cephamins, penicillins, clindamycin, and metronidazole in the United States.

Over 2800 clinical strains of the Bacteroides fragilis group were collected during a 5-year period from ten geographically separate sites and tested for their susceptibility to various antimicrobial agents using a broth microdilution method. Among the cephalosporins, ceftizoxime was the most active (13% resistance) and importantly exhibited relatively equal activity against both B. fragilis species and non-B. fragilis species. Cefotaxime exhibited similar activity with an overall resistance rate of 18%. Both ceftriaxone and cefoperazone were appreciably less active cephalosporins especially against non-B. fragilis species. With regard to cephamycins, cefoxitin (MIC90, 32 micrograms/ml) was more active than cefotetan (MIC90, > or = 256 micrograms/ml) and cefmetazole (MIC90, 64 micrograms/ml). Non-B. fragilis species were highly resistant to cefotetan and cefmetazole. Imipenem was highly active against all strains with the exception of four strains of B. fragilis. Ampicillin-sulbactam, amoxicillin-clavulanate, piperacillin-tazobactam, and cefoperazone-sulbactam were all highly active with resistance rates < 2%. No resistance was detected to metronidazole, whereas 14% of isolates were resistant to clindamycin. When compared with other studies, these findings underscore the wide variability in susceptibility patterns reported nationwide and the need to continue monitoring these patterns to aid in choosing the most active compounds for therapy.

TORCH serologies and specific IgM antibody determination in acquired and congenital infections.

Except for rubella testing, routine TORCH serology screens in prenatal care are of little use. Individual TORCH tests may, however, be useful based on the clinical presentation and history of the patient. The laboratory test of choice for diagnosing cytomegalovirus (CMV) and herpes simplex virus (HSV) infections is culture isolation for the virus. The presence for specific IgM antibodies in neonates is diagnostic of congenital infection. In adults, IgM antibody results should be interpreted along with the clinical findings and history of the patient. IgM antibodies may persist for months and even years and may be detected during reactivation of latent virus infections. Serum fractionation should always be performed in IgM antibody testing to avoid false positive results owing to rheumatoid factors and false negative results owing to competing levels of specific IgG antibodies. With a single serum specimen, specific IgM antibody detection may be helpful in differentiating between a recent versus past infection.

Comparison of rapid methods of antimicrobial susceptibility in Haemophilus influenzae.

A method is described for the rapid, simultaneous determination of the MIC's of chloramphenicol and ampicillin to Haemophilus influenzae. Excellent agreement was observed between the Autobac method and the agar dilution method for antimicrobial susceptibility. All ampicillin resistant Haemophilus isolates produced beta lactamase and none of the suceptible strains produced this enzyme.

Quantitative antibiotic susceptibility testing: Haemophilus influenzae type B.

Twelve strains of Haemophilus influenzae were tested for susceptibility to gentamicin, ampicillin, chloramphenicol and cephalothin using two methods, agar dilution and microdilution (broth). Although inocula and incubation conditions were standardized, significant differences in the minimal inhibitory concentration (MIC) were seen as a result of growth media. Method dependent differences were also observed for some antibiotics. Notwithstanding such variation, high level resistance of H. influenzae to ampicillin was readily detected by either broth or agar dilution tests.

Inhibition of bacterial growth by granulocytes measured by an automated technique.

Granulocytes, collected by several methods, were assayed for antibacterial activity utilizing a technique originally developed for automated antibiotic susceptibility testing. The granulocytes were incubated with either Escherichia coli or Staphylococcus for one hour at 37 degrees C and were then separated from the suspension by gentle centrifugation at 170 g. The bacteria remaining in the supernatant broth were incubated in culture medium (eugonic broth) and their growth density was compared with diluted controls (without granulocytes) by measurement in an Autobac I (an automated nephelometer). Measurements of the density of growth at 30 minute intervals showed a marked delay in the development of density suggesting only small numbers of organisms remained after incubation with granulocytes. Once density was measurable, the rate of growth appeared similar to controls. After 2.5 hours in the Atuobac I, the density of growth was used to determine the inhibitory effect of granulocytes. The density of growth was inversely related to the concentration of granulocytes present during the preincubation phase. Filtered granulocytes showed significantly lower inhibitory effect than centrifuged granulocytes. This rapid, inexpensive method of determining microbial growth appears to be adaptable as a measure of granulocyte function.

Gentamicin-carbenicillin synergy among gentamicin resistant Pseudomonas aeruginosa.

Forty-five isolates of gentamicin resistant Pseudomonas aeruginosa were evaluated for gentamicin-carbenicillin synergy. Only 9 percent (4/45) showed synergy. Of nine isolates with demonstrable zones around a gentamicin disc (8 to 12 mm), none showed a synergistic response. Effective treatment of gentamicin resistant Ps. aeruginosa with gentamicin and carbenicillin should not be assumed without additional test procedures.

Utility of a rapid latex test for the detection of Clostridium difficile in fecal specimens.

Currently, the method of choice for the laboratory diagnosis of Clostridium difficile disease is the detection of cytotoxin in stool filtrates by tissue culture. Since many hospital laboratories do not have tissue culture facilities, there is a need for a rapid test which is both sensitive and specific to diagnose C. difficile disease. A commercial latex agglutination was compared with the conventional cytotoxin tissue culture assay for the detection of C. difficile or its toxin(s) in fecal specimens. Of the 574 specimens evaluated, 111 were cytotoxin positive while 97 were positive by the latex agglutination test. There were 17 specimens positive by latex agglutination but negative by tissue culture assay. The overall sensitivity and specificity of the CDT latex test was 86.1 percent and 95.3 percent respectively. This rapid latex test can serve as an excellent screening procedure for the presence of C. difficile. Those specimens positive by the latex test should be further evaluated for the presence of cytotoxin by tissue culture.

The rapid detection of clinically significant bacteria.

In summary, there are a variety of methods for the rapid detection of bacteria, only a few of which have been covered in this essay. However, 3 points must be made: 1) The availability of a test for antigen detection does not guarantee its clinical relevance. 2) More attention must be paid to the statistical relevance of tests for bacterial detection. 3) The advantages of a rapid test compared to a very lengthy traditional test for bacterial detection may not be obvious unless there is an organized method of education and accompanying justification, such as treatment efficacy, for the use of this new test.