Application of alternative fixatives to formalin in diagnostic pathology.

Fixation is a critical step in the preparation of tissues for histopathology. The objective of this study was to investigate the effects of different fixatives vs formalin on proteins and DNA, and to evaluate alternative fixation for morphological diagnosis and nucleic acid preservation for molecular methods. Forty tissues were fixed for 24 h with six different fixatives: the gold standard fixative formalin, the historical fixatives Bouin and Hollande, and the alternative fixatives Greenfix, UPM and CyMol. Tissues were stained (Haematoxylin-Eosin, Periodic Acid Schiff, Trichromic, Alcian-blue, High Iron Diamine), and their antigenicity was determined by immunohistochemistry (performed with PAN-CK, CD31, Ki-67, S100, CD68, AML antibodies). DNA extraction, KRAS sequencing, FISH for CEP-17, and flow cytometry analysis of nuclear DNA content were applied. For cell morphology the alternative fixatives (Greenfix, UPM, CyMol) were equivalent to formalin. As expected, Hollande proved the best fixative for morphology. The morphology obtained with Bouin was comparable to that with formalin. Hollande was the best fixative for histochemistry. Bouin proved equivalent to formalin. The alternative fixatives were equivalent to formalin, although with greater variability in haematoxylin-eosin staining. It proved possible to obtain immunohistochemical staining largely equivalent to that following formalin-fixation with the following fixatives: Greenfix, Hollande, UPM and CyMol. The tissues fixed in Bouin did not provide results comparable to those obtained with formalin. The DNA extracted from samples fixed with alternative fixatives was found to be suitable for molecular analysis.

Detection of high risk HPV and Chlamydia trachomatis in vaginal and cervical samples collected with flocked nylon and wrapped rayon dual swabs transported in dry tubes.

A dual collection device containing flocked and wrapped rayon swabs was used to collect vaginal and cervical samples from 494 women. The swabs were separated into individual tubes and sent to the laboratory in a dry state, where they were hydrated and tested for high risk HPV DNA [Digene-Qiagen hybrid capture 2] and Chlamydia trachomatis using in-house real-time PCR. The flocked swabs identified more high risk HPV and C. trachomatis infections from both sampling sites.

Accuracy of results obtained by performing a second ligase chain reaction assay and PCR analysis on urine samples with positive or near-cutoff results in the LCx test for Chlamydia trachomatis.

Nucleic acid amplification assays such as the ligase chain reaction and PCR have encountered reproducibility problems. The initial extract and a newly extracted aliquot of urine specimens (n = 120) which had signal-to-cutoff (S/CO) ratios above 0.80 by the LCx Chlamydia assay were retested. Nucleic acid was extracted from an additional urine sample for testing by the AMPLICOR PCR Chlamydia assay. Fifteen percent (18 of 120) of the urine specimens were negative by all repeat tests (initial mean S/CO ratio by the LCx Chlamydia assay, 0.93; S/CO ratio range, 0.80 to 3.30). Repeat testing of the 102 specimens with possible positive results by the LCx Chlamydia assay by use of the initially extracted aliquot confirmed the results for 95 (93.1%) of the specimens; repeat testing of a newly extracted aliquot confirmed the results for 87 (85.3%) of the specimens. Twenty specimens had discordant results by the two repeat LCx Chlamydia assays. A total of 78 of 102 (76.5%) of the specimens were positive by the AMPLICOR PCR, and the AMPLICOR PCR confirmed the results for 82.1% (78 of 95) and 89.6% (78 of 87) of the specimens positive by the two repeat LCx Chlamydia assays, respectively. Some of the discrepancies observed by multiple repeat tests may have been due to specimen mislabeling or contamination during performance of the procedure rather than to the LCx Chlamydia assay. Both assays suffered from a lack of reproducibility on repeat testing with a small proportion of specimens, probably due to the presence of low levels of DNA, the presence of variable amounts of amplification inhibitors, and the loss of DNA during extraction.

Urinary inhibitors of polymerase chain reaction and ligase chain reaction and testing of multiple specimens may contribute to lower assay sensitivities for diagnosing Chlamydia trachomatis infected women.

In a comparison of commercial ligase chain reaction (LCR; Abbott) and polymerase chain reaction (PCR; Roche) assays, measuring plasmid genes of Chlamydia trachomatis, some specimens were found to be negative by either or both assays but positive in traditional culture or antigen detection tests. Of 767 women, 35 were found to be infected by cervical or urine testing. Twenty three specimens from 16 women may have contained inhibitors in six cervical swabs (CS) and 15 first void urines (FVU). By performing dilution and 'spiking' experiments on five FVU, inhibitors of PCR, LCR or both, which disappeared by dilution, were demonstrated. Confirmatory assays were used which amplified segments of the major outer membrane gene by PCR or LCR. When comparisons of assays were made on a single specimen type, the sensitivities of the amplification assays, compared to an expanded reference standard, were as follows: on CS, PCR was 93.8% (30/32) and LCR was 96.9% (31/32); on FVU, PCR was 76.6% (23/30) and LCR was 93.3% (28/30). When a combined calculation was made to determine the ability of the assays to detect patients infected in the cervix or urethra by testing FVU, the sensitivities dropped to 71.4% (25/35) for PCR and 80.0% (28/35) for LCR: CS sensitivity was 88.6% (31/35) for both amplified tests. There were two CS and five FVU false-positives by PCR which reduced to one CS and three FVU in the combined analysis. There were no false-positives by LCR. Inhibitors and low levels of chlamydial plasmid nucleic acids may have contributed to lower than expected sensitivities, suggesting a possible need for internal positive controls, especially for PCR, when testing urine. More studies with multiple sampling and more than one amplification assay are needed to confirm these findings and to identify and remove inhibitors of amplification assays.

Performance characteristics of recombinant enzyme immunoassay to detect antibodies to human immunodeficiency virus type 1 (HIV-1) and HIV-2 and to measure early antibody responses in seroconverting patients.

We investigated the performance of a double-antigen sandwich recombinant enzyme immunoassay (EIA; Abbott Laboratories, North Chicago, Ill.) and compared it with that of a synthetic-peptide-based EIA (Biochem Immunosystems, Montreal, Quebec, Canada) for the detection of human immunodeficiency type 1 (HIV-1) and HIV-2 antibodies in 2,321 clinical serum samples. The results of both EIA methods and Western blot (immunoblot) were in agreement for 1,046 HIV-1 and 10 HIV-2 specimens from a panel of known positives. From a prospective panel of 1,085 specimens, 38 proved to be positive by both EIAs and Western blot, 3 were positive by the recombinant EIA only, and 9 were positive by the peptide EIA only, for calculated specificities of 99.71 and 99.04%, respectively. Of 180 specimens from a seroconversion panel collected from 77 patients, the results for 170 were in agreement by all antibody testing methods and 10 were found to be repeat reactive for HIV antibodies by the recombinant EIA only. All 10 were initial specimens of seroconverting patients; 7 were also reactive for HIV p24 antigen. An examination of four of these sera by radioimmunoprecipitation assay showed gp120 and gp160 bands in each. Analysis of the anti-Env antibody class in three of these samples showed that one consisted of immunoglobulin M (IgM) only and two contained both IgG and IgM antibodies. Although both EIA procedures were sensitive and specific in the detection of antibodies to HIV-1 and HIV-2 and both were capable of detecting early antibodies, the recombinant assay was more sensitive for antibody detection during early seroconversion.

Confirmatory testing demonstrates that false-positive rates in the chlamydiazyme assay are influenced by gender and genital specimen type.

BACKGROUND AND OBJECTIVES: Chlamydia trachomatis antigen testing of clinical specimens is replacing culture as the test of choice. Because of a potential for false positive results in low prevalence populations, there is an apparent need for confirming specimens positive by enzyme immunoassay (EIA). GOAL OF THIS STUDY: To examine specimens falsely positive in the Chlamydiazyme EIA assay according to gender and specimen type. STUDY DESIGN: Testing of genitourinary specimens from men and women consecutively enrolled from five health care delivery sources in an urban Canadian population. All specimens were initially tested in the Chlamydiazyme test and all positives repeated in a confirmatory blocking assay provided by the manufacturer. Additional confirmatory testing was performed using immunofluorescence (IF) staining for C. trachomatis elementary bodies (EB's) and polymerase chain reaction (PCR). RESULTS: From Jan. 1, 1990 to June 1, 1991, multiple specimens from 656 men and 5,628 women of varying population prevalences were screened. EIA-positive specimens from women had a repeat negative rate of 22% to 27% from cervical swabs and 29% from urethral swabs. Male urethral swabs had a high repeat negative rate of 22% when EIA was the only positive test, but 2.4% when the specimen was positive by EIA and culture. EIA-positive first void urine (FVU) specimens from men had a repeat negative rate of 8.7% as opposed to 17% to 32% from women. Only 1.7% (2/115) of male FVU did not block compared to rates of 47% (22/47) to 80% (4/5) in FVU from women. Analysis of EIA optical densities (OD's) and EB counts showed an association between the absorbance range 0.1 to 1.4 OD and 0-85 EB's. The greatest number of EB's and highest OD's were seen with cervical specimens, followed by urine and urethral specimens in women infected at all three specimens. All 55 specimens that did not confirm in the blocking test had no EB's and a convenience sample of seven were negative by PCR. All of a subset of 50 blocked specimens contained EB's or were positive by PCR. CONCLUSIONS: Although a variable proportion of specimens may not repeat positive in the EIA, use of the blocking reagent to confirm the repeat positives is highly recommended and the rate of blocking may be heavily influenced by gender and specimen type.

Immunogenicity and adverse reactions of influenza vaccination in elderly patients given acetaminophen or placebo.

The objective was to examine the antibody responses to influenza immunization in an elderly population and the effect of prophylactic acetaminophen on adverse responses due to inactivated whole virus vaccine containing influenza A (H3N2 and H1N1) and B antigens. During the autumn of 1990, 100 patients 65 years or older were immunized and randomly allocated to receive placebo or 1,950 mg (2 x 975 mg) of acetaminophen. They recorded any local and systemic side effects over a 3-day period. Serology was performed on pre- and post (4-6 weeks) -vaccination sera. Age and gender distribution in the study were: 47% who were 75 years or older, and 61% of the patients were female. Most of the patients (97%) had pre-existing antibodies to Influenza A or B. Average peak preimmunization antibody titers were 40 to B Yamagata and A Taiwan (H1N1) and 80 for A Shanghai (H3N2). Half of each treatment group had a 4-fold or greater rise in antibody titer in response to the vaccine. Only 30% of patients immunized the previous year but 80% of those never vaccinated previously demonstrated a 4-fold or greater serological response to the vaccine. However, measurement of protection rates (HI >/= 40) before and after vaccination indicated 81.1-100% protection for the 3 viruses not influenced by treatment, gender or a history of previous vaccination. Both treatment groups had equally small numbers of patients who recorded systemic symptoms of drowsiness, myalgia, fever and chills and about 50% had arm soreness. Although about 80% of previously unimmunized adults mounted a 4-fold antibody rise to influenza vaccine antigens whereas booster effects were seen in only 30% of those immunized the previous year, protection rates were high (81-100%) after immunization and were not affected by acetaminophen treatment. Adverse effects (15% systemic and 50% local) were not ameliorated by 1950 mg of acetaminophen in these elderly patients.

The diagnosis of acute viral hepatitis A or B by microparticle enzyme immunoassay.

The traditional approach to the diagnosis of viral hepatitis has been to collect a serum sample and to test it for the presence of hepatitis B surface antigen (HBsAg), IgM to the core of HBV (anti-HBc IgM) and IgM to HAV (anti-HAV IgM) by solid phase radio- or enzyme immunoassays. Microparticle enzyme immunoassay technology (IMx-Abbott Laboratories) has been introduced as an automated carousel system for the detection of these markers. A side-by-side, blinded comparison of IMx to current IA was performed for HBsAg on 659 specimens submitted from March to July 1990, of which 72 (10.8%) were positive by AUSRIA (Abbott RIA for HBsAg) and 2 of these were discordant in IMx. Both were near the cutoff and by confirmatory testing one was positive and the other negative. Forty three percent (25/58) of frozen stored sera tested for anti-HBc IgM, by IMx, were positive by EIA (Corzyme M). One specimen near the cutoff was negative by EIA but weakly positive by IMx. Anti-HAV IgM was found in 21.8% (46/211) of sera with 100% correlation by IMx. Thus IMx had the following percent sensitivies and specificities: HBsAg; 98.6, 99.9; anti-HBc IgM; 100, 99.9; anti-HAV IgM; 100, 100. The test set-up times for the 3 markers in the IMx were similar to the RIA and EIA. The turnover time was 45 min for a full IMx carousel compared to: AUSRIA-short incubation (4 h), or long incubation (14 h); Corzyme M-short (4.75 h) or long (20 h); anti-HAV IgM (23 h).(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of a pregnancy-screening and neonatal-immunization program for hepatitis B in Hamilton, Ontario, Canada, 1977-1988.

During the 12 years from January, 1977, to December, 1988, the Hamilton Centre of the Canadian Red Cross Society (CRCS) Blood Transfusion Service screened 98,712 pregnant patients for hepatitis B surface antigen (HBsAg) and identified 120 positives (0.12%). The number of positives ranged from six to 16 per year. We were able to trace and enroll 65 mothers (54%) and 96 of their children in the follow-up study. The majority of the women were between 20 and 30 years of age (95.4%) and married (86%), and about one-half were employed outside the home. Sixty-five percent were white and 34% Asian, and 20 countries were listed as their places of origin. Hepatitis B immune globulin (HBIG) was available for neonatal immunization since 1977 and combined with vaccine since 1982. Of the 96 candidates for HBIG, 60 (63%) received HBIG within 24 hr, one after 3 months, four unknown, and 31 did not receive it. Of the 56 candidates for vaccination from 1982 to 1989, 26 (46%) received three doses, seven had two doses, eight had one dose, one was unknown, and 14 had none. HBsAg tests were performed on 69 children (71.8%) and anti-HBs on 61 (63.5%). Four of the children are HBsAg positive, 31 have anti-HBs, and 31 have no detectable antibodies. All four HBsAg positives had not received vaccine, and only one had received HBIG. Of the children positive for hepatitis B surface antibodies, five had received no immunization and therefore had been subclinically infected.(ABSTRACT TRUNCATED AT 250 WORDS)

Rapid, on-site diagnosis of chlamydial urethritis in men by detection of antigens in urethral swabs and urine.

First-void urine (FVU) sediments of 240 men were tested for Chlamydia trachomatis antigens by two enzyme immunoassays, TestPack Chlamydia (15 min) and Chlamydiazyme (3.5 h), and the results were compared with urethral swab culture results. The sensitivity and specificity on FVU sediment for TestPack Chlamydia were 76.2% (32 of 42 specimens) and 95.5% (189 of 198 specimens) versus 81.0% (34 of 42 specimens) and 96.5% (191 of 198 specimens) for Chlamydiazyme, respectively. Rapid, on-site detection of chlamydial antigen in male FVU would shorten the infectious period by hastening diagnosis and treatment.

Detection of Chlamydia trachomatis antigens in urine as an alternative to swabs and cultures.

By using commercially available spectrophotometric and immunofluorescent immunoassays, Chlamydia trachomatis antigens were detected in first-void urine (FVU) sediments from 224 men attending a sexually transmitted disease clinic at a frequency of 81.6%-86.8% compared with 86.8% (33/38) positive by urethral swab culture (P less than .05). Endocervical cultures from 228 women attending a gynecology clinic yielded 92.3% (12/13) positive compared with 61.5%-76.9% for urine samples in three antigen-detection assays. Culturing urine from either gender yielded low positivity rates (23.7% for men, 15.4% for women). Defining truly infected patients as positive by culture or by any two of the three antigen tests, all assays were 100% specific. Immunodiagnostic testing of male FVU sediment appears to be a reliable, rapid, nontraumatic method for diagnosing chlamydia infection.

A clinical virology database for a regional virology service.

We describe a laboratory information system employing a virus and chlamydia database developed over seven years which is used by a regional laboratory, performing virus and chlamydia testing. The information system is implemented on a University mainframe computer and accessed by computer terminals in the laboratory. The database is used to identify patients, store patient test results, minimize clerical work and improve accuracy of reported results. The database also serves as a patient registry for use in education and research.

Diagnosis of Chlamydia trachomatis genital infections by cell culture and two enzyme immunoassays detecting different chlamydial antigens.

The enzyme-amplified immunoassay IDEIA (CellTech Diagnostics), which measures lipopolysaccharide antigen, and Chlamydiazyme (Abbott Laboratories, North Chicago, Ill.), which measures several antigenic components of Chlamydia trachomatis, were compared for specimens from urethral swabs from 235 men attending a clinic for sexually transmitted diseases (culture prevalence of 14.9%) and 458 endocervical swabs from women attending planned parenthood and obstetrics-gynecology clinics (culture prevalences of 5.9 and 7.7%, respectively). Compared with cell culture, the percent sensitivites, specificities, and positive and negative predictive values for IDEIA were 62.5, 99.5, 95.2, and 94.3%, respectively, for specimens from men and 96.3, 97.9, 74.3, and 99.8%, respectively, for specimens from women; results for Chlamydiazyme for specimens from men were 81.8, 99.5, 96.4, and 97.1%, respectively, and for specimens from women, results were 85.2, 99.3, 88.5, and 99.1%, respectively. Although the specificities of IDEIA and Chlamydiazyme were comparable, the sensitivity of IDEIA appeared higher for women (96.3%) than for men (67.5%), while the sensitivities of Chlamydiazyme were similar for men (81.8%) and women (85.2%). Western blot (immunoblot) analysis of the detector reagents from the two immunoassays indicated that the differences in performance observed for the two immunoassays may be due to measurement of different antigens.

Agreement study between two laboratories of immunofluorescence as a confirmatory test for human immunodeficiency virus type 1 antibody screening.

A total of 114 serum specimens from 76 blood donors, 21 patients with acquired immune deficiency syndrome or acquired immune deficiency syndrome-related complex, 7 multiply transfused patients, 3 hemophiliacs, and 7 others were tested for anti-human immunodeficiency virus type 1 (HIV-1) antibody by enzyme immunoassay (EIA) and Western blot (WB) and then blindly tested by immunofluorescence (IF), independently, in two separate laboratories. The IF technique used acetone-fixed HIV-1-infected E cells and uninfected HUT-78 cells mixed at a 1:3 ratio in one spot on a glass slide and uninfected HUT-78 cells (to assess nonspecific fluorescence) alone in a second spot. Of 114 serum specimens, 85 were repeat EIA positive, and 21 of these were WB positive. A total of 129 of 134 of the IF results (included were 20 duplicates) were identical between laboratories, for a Kappa agreement statistic of 0.93. All five IF results discordant between laboratories were EIA repeat positive and WB negative. Included in the study were eight WB-indeterminate sera, of which five blood donor serum specimens and one hemophiliac serum specimen were IF negative and two acquired immune deficiency syndrome serum specimens were IF positive. As a confirmatory test for HIV-1 antibodies, IF provided a faster alternative or supplementary test for confirming EIA results.

Nasopharyngeal swabs and nasopharyngeal aspirates equally effective for the diagnosis of viral respiratory disease in hospitalized children.

Paired nasopharyngeal swab and nasopharyngeal aspirate specimens from 125 patients were compared for viral diagnosis. The viral isolation rates were comparable for the two types of specimens. There was a high level of agreement between the two specimens in overall positivity rate by immunofluorescence and positivity in culture-confirmed patients.

Ability of TESTPACK ROTAVIRUS enzyme immunoassay to diagnose rotavirus gastroenteritis.

TESTPACK ROTAVIRUS, a simple 10-min enzyme immunoassay, was compared with electron microscopy and Pathfinder enzyme immunoassay on feces from 172 patients of various ages with gastroenteritis. The percent sensitivities and specificities before blocking with antiserum were as follows: TESTPACK, 100% sensitivity and 99% specificity; Pathfinder, 95% sensitivity and 98% specificity. After blocking, the sensitivity and specificity, respectively, were 100% and 100% for TESTPACK and 95% and 99% for Pathfinder. TESTPACK ROTAVIRUS was more sensitive, but not significantly, than Pathfinder (P greater than 0.1) and the direct electron microscopy technique (P greater than 0.1).

Cost and performance analysis of haemagglutination inhibition, passive haemagglutination, radial haemolysis, and enzyme immunoassay for measuring rubella antibody.

Cost and performance of non-commercial haemagglutination inhibition (HI) and radial haemolysis (RH) tests, and the commercially available passive haemagglutination (PHA) Rubacell and enzyme immunoassay (EIA) and Rubazyme assays were compared in their ability to detect rubella antibodies in 316 sera. Correlation coefficients were: HI to RH 0.96; HI to EIA 0.86. All 4 tests were in agreement on pre- and post-rubella immunization sera from 10 subjects. Eleven sera collected between 1 and 15 days after natural infection possessed clear HI titres whereas only 4 of them showed positive responses by PHA, RH or EIA. Immunity screening 285 sera identified 7 discordant results (positive in 2 of 4 tests). A detailed cost analysis for testing 100 sera showed a cost per test from +2.10 for HI to +3.71 for EIA. The labour component of the total cost was different for each assay and affected the unit cost of testing a single specimen. Results are discussed in view of antibody responses to specific rubella polypeptides and recommendations for diagnosis or immunity screening are made according to the findings.

Combined testing for antibodies to rubella non-structural and envelope proteins sentinels infections in two outbreaks.

Two separate outbreaks of Rubella occurred in Hamilton, Ontario, Canada, 7 yrs apart, with a peak incidence for both in the month of April. A total of 138 cases, 51 in 1978 and 87 in 1985, was observed, the majority being in adolescents and young adults 15-25 years of age. Cases were diagnosed by the presence of Rubella IgM antibody or the combination of a negative passive hemagglutination (Rubacell-Abbott) and a positive enzyme immunoassay (EIA) or hemagglutination inhibition (HI) test on a single serum or by seroconversion for Rubella IgG antibody. Routine screening of sera with the Rubacell test, which measures antibodies to nonstructural rubella proteins together with HI or EIA testing of the negatives, served as a sentinel for rubella infection in the community during both outbreaks. Rubacell antibodies usually appeared 2-3 wk after onset of infections, and when present contained either or both IgG and IgM. Only 8/103 cases had a history of Rubella vaccination. Two of three products of conception yielded rubella virus in cell culture.

Diagnostic significance of anti-HBcIgM prevalence related to symptoms in Canadian patients acutely or chronically infected with hepatitis B virus.

A total of 362 sera from 295 Canadian patients were examined for HBsAg, anti-HBs, anti-HBc, anti-HBcIgM, HBeAg, and anti-HBe using commercial immunoassays. Serial samples from 70 acutely infected patients demonstrated that anti-HBcIgM may detect 10% more positives than HBsAg within 4 months after the onset of clinical symptoms, and all except two were negative for anti-HBcIgM after the fourth month. None of 66 asymptomatic (HBeAg rate 18.2%) and two of 14 (14.3%) symptomatic (HBeAg rate 64.3%) carriers of HBsAg were positive for anti-HBcIgM (P = 0.029). Elevated marker responses were measured in two symptomatic carriers for a 20-month period. Anti-HBcIgM was not detected in either 100 asymptomatic patients positive for total anti-HBc, negative for HBsAg and negative for or possessing low levels of anti-HBs, 25 patients with liver disorders not caused by HBV, or 20 healthy milk donors. In diagnostic laboratory practice this anti-HBcIgM test may be useful in the following situations: to supplement HBsAg testing, providing a theoretical 10% increase in positives within 4 months following onset of acute viral hepatitis; to replace testing for anti-HBc and anti-HBs in symptomatic HBsAg-negative patients; to confirm whether a patient is experiencing acute or chronic HBV infection or symptoms superimposed upon asymptomatic HBsAg carriage by another cause, such as nonA-nonB viral hepatitis.

Detection of Chlamydia trachomatis antigens by enzyme immunoassay and immunofluorescence in genital specimens from symptomatic and asymptomatic men and women.

Chlamydia trachomatis antigens were detected in populations with the following infection prevalences: 26.5% (36 of 136) of men and 27.7% (48 of 173) of women attending a sexually transmitted disease clinic, 16.3% (53 of 324) of women attending a Planned Parenthood clinic, and 3.4% (4 of 117) of an obstetrics and gynecologic practice. Compared with cell culture of the combined female cervical specimens (15.8% prevalence), the respective sensitivities of Chlamydiazyme (Abbott Laboratories, North Chicago, Illinois) and Microtrak (Syva, Palo Alto, California) were 98.3% and 87.9%, specificities were 97.5% and 98.4%, positive predictive values were 87.7% and 92.7%, and negative predictive values were 99.7% and 97.5%. Both assays were 70.0% sensitive with male urethral specimens, and the other parameters of performance ranged between 84.0% and 97.2%. The antigen detection assays, compared with culture, performed equally well in subjects without or with clinical signs.