Heterophilic interference in specimens yielding false-reactive results on the Abbott 4th generation ARCHITECT HIV Ag/Ab Combo assay

BACKGROUND

False-reactivity in HIV-negative specimens has been detected in HIV fourth-generation antigen/antibody or 'combo' assays which are able to detect both anti-HIV-1/HIV-2 antibodies and HIV-1 antigen.

OBJECTIVES

We sought to characterize these specimens and determine the effect of heterophilic interference.

STUDY DESIGN

Specimens previously testing as false-reactive on the Abbott ARCHITECT HIV Ag/Ab combo assay and re-tested on a different (Siemens ADVIA Centaur HIV Ag/Ab) assay. A subset of these specimens were also pre-treated with heterophilic blocking agents and re-tested on the Abbott assay.

RESULTS

Here we report that 95% (252/264) of clinical specimens that were repeatedly reactive on the Abbott ARCHITECT HIV Ag/Ab combo assay (S/Co range, 0.94-678) were negative when re-tested on a different fourth generation HIV combo assay (Siemens ADVIA Centaur HIV Ag/Ab). All 264 samples were subsequently confirmed to be HIV negative. On a small subset (57) of specimens with available volume, pre-treatment with two different reagents (HBT; Heterophilic Blocking Tube, NABT; Non-Specific Blocking Tube) designed to block heterophilic antibody interference either eliminated (HBT) or reduced (NABT) the false reactivity when re-tested on the ARCHITECT HIV Ag/Ab combo assay.

CONCLUSIONS

Our results suggest that the Abbott ARCHITECT HIV Ag/Ab combo assay can be prone to heterophilic antibody interference.

Unique combined penA/mtrR/porB mutations and NG-MAST strain types associated with ceftriaxone and cefixime MIC increases in a 'susceptible' Neisseria gonorrhoeae population

OBJECTIVES

To determine which mutations in penA, mtrR and porB are implicated in increasing minimum MICs of ceftriaxone and cefixime in a susceptible gonococcal population and to ascertain associations with gonococcal strain types (STs).

METHODS

One hundred and forty-six Neisseria gonorrhoeae isolates formed two extended-spectrum cephalosporin susceptibility groups: group 1 isolates with cefixime and ceftriaxone MICs of 0.0005-0.016 mg/L; and group 2 isolates with cefixime MICs of 0.03-0.125 mg/L (n = 24) and ceftriaxone MICs of 0.03-0.06 mg/L (n = 23). Mutation patterns in penicillin-binding protein 2 (PBP2; penA), multiple transfer resistance repressor (MtrR; mtrR) and porin B (PorB; porB) were ascertained by DNA sequence and bioinformatic analysis. STs were determined using N. gonorrhoeae multiantigen sequence typing (NG-MAST).

RESULTS

Most isolates carried PBP2 mutation pattern IX (D345a, F504L, A510V, A516G and P551L; 50/146, 34.2%), a G45D substitution in MtrR (37.7%) and a wild-type (WT) sequence for PorB (43.2%). Group 2 gonococcal isolates were significantly associated with: penA pattern IX; dual mutations in the promoter (A-) and DNA dimerization domain (H105Y) of MtrR; and G120K;A121D substitutions in PorB. There were 50 combined penA/mtrR/porB mutation patterns, with corresponding patterns I/WT/WT and IX/G45D/G120K;A121D predominating. Gonococci susceptible to ceftriaxone and cefixime were significantly associated with NG-MAST ST 25 (33/36; 92%) and the combined penA/mtrR/porB mutation pattern I/WT/WT. No combined mutation pattern or specific ST was associated with elevated ceftriaxone MICs. NG-MAST ST 3654 was significantly associated with the pattern IX/G45D/G120K;A121D and cefixime group 2 isolates.

CONCLUSIONS

Specific single or combined mutation patterns in penA, mtrR and porB and specific STs were associated with differences in susceptibility to ceftriaxone and cefixime.

Classification of Leptospira genomospecies 1, 3, 4 and 5 as Leptospira alstonii sp. nov., Leptospira vanthielii sp. nov., Leptospira terpstrae sp. nov. and Leptospira yanagawae sp. nov., respectively

The genus Leptospira currently comprises 16 named species. In addition, four unnamed hybridization groups were designated Leptospira genomospecies 1, 3, 4 and 5. These groups represent valid species-level taxa, but were not assigned names in the original description by Brenner et al. [Int J Syst Bacteriol 49, 839-858 (1999)]. To rectify this situation, it is proposed that Leptospira genomospecies 1, genomospecies 3, genomospecies 4 and genomospecies 5 should be classified as Leptospira alstonii sp. nov., Leptospira vanthielii sp. nov., Leptospira terpstrae sp. nov. and Leptospira yanagawae sp. nov., respectively, with strains L. alstonii 79601(T) ( = ATCC BAA-2439(T)), L. vanthielii WaZ Holland(T) ( = ATCC 700522(T)), L. terpstrae LT 11-33(T) ( = ATCC 700639(T)) and L. yanagawae Sao Paulo(T) ( = ATCC 700523(T)) as the type strains. The type strains are also available from the culture collections of the WHO Collaborating Centres in Amsterdam, The Netherlands, and Brisbane, Australia.

A quantitative risk assessment of West Nile virus introduction into Barbados

OBJECTIVE

To present a quantitative risk assessment of West Nile (WNV) virus introduction into Barbados, West Indies.

DESIGN AND METHODS

Three possible modes were considered: a) WNV infected mosquitoes via air transport, by city of departure, b) WNV infected mosquitoes via marine transport and c) viraemic migratory, birds. We estimated the number of WNV infected migratory birds as the product of the proportion of migratory birds infected and the number of migratory birds entering Barbados in three taxonomic groups. We further estimated the number of days these birds would be infectious as: [formula: see text]. We then estimated the number (#) of infectious mosquito-days for mosquitoes entering Barbados via air transport as: # infected mosquitoes = (total flights per week/city) x (duration of WNV season) x (number of Culex mosquitoes aboard each flight) x (Culex mosquito WNV infection prevalence) x (vector competence index) x (days infectious). The number of infected mosquitoes entering Barbados via marine transport was estimated using a similar expression as for air transport, except that the number of airplanes and mosquitoes/airplane were substituted with the # of sea containers during a 22-week mosquito season and # of mosquitoes/container.

RESULTS

Migratory birds (approximately 69-101 infected birds/year) were associated with the highest introductory risk followed by mode (a) (approximately 2 infected mosquitoes/year) and mode (b) (0. 004 infected mosquitoes/year).

CONCLUSIONS

Migratory birds and mosquitoes via air are imminent threats for virus introduction. Impending co-circulation of West Nile virus and four strains of dengue virus may present new challenges for public health.

Evaluation of a commercial latex agglutination assay for serological diagnosis of leptospirosis

Leptospirosis is a febrile zoonosis of worldwide distribution. A latex agglutination assay was evaluated in two studies, the first using a panel of well-characterized sera from patients with leptospirosis and from patients with other disease states and the second, a prospective hospital-based study, evaluating sera from 186 consecutive patients admitted to hospital with acute febrile illness. The confirmed leptospirosis serum panel included paired acute- and convalescent-phase specimens from 40 cases, of which 34 gave positive latex tests (case sensitivity, 85%; 95% confidence interval [95% CI], 70 to 94%). The other diseases represented in the panel of 112 specimens from nonleptospirosis patients included autoimmune diseases, brucellosis, dengue, melioidosis, malaria, syphilis, toxoplasmosis, viral hepatitis, and a number of other viral infections. The specificity of latex agglutination using this panel was 81% (95% CI, 73 to 87%). Among the patients with acute febrile illness, there were 25 cases of leptospirosis and 161 patients with other diagnoses. The sensitivity and specificity of latex agglutination in this group were 88% (95% CI, 72 to 97%) and 98% (95% CI, 95 to 100%), respectively. In this evaluation, the two distinct groups of specimens gave similar results for sensitivity, but specificity was different in each study. The sensitivity and specificity observed for the hospital study were similar to those obtained in evaluations of other rapid tests in the same population. The results of this study suggest that multiple evaluations of new diagnostic assays should be performed, because performance characteristics may vary in different populations.

Use of immunoglobulin G avidity assays for differentiation of primary from previous infections with West Nile virus

Since its introduction in 1999, West Nile virus (WNV) infections have spread rapidly across the North American continent. Diagnosis of acute WNV infection by detection of WNV-specific immunoglobulin M (IgM) is complicated by the persistence of detectable IgM for more than 1 year in some patients. IgG antibody avidity testing was assessed as a supplemental assay in the diagnosis of current infections. Three groups of serum samples were assayed in parallel by two different IgG avidity test systems (indirect immunofluorescence test [IIFT] and prototype enzyme-linked immunosorbent assay [ELISA]; EUROIMMUN, Luebeck, Germany). Group I (40 sera taken between 2 and 9 days after the onset of influenza-like symptoms) and group II (40 sera taken between 10 and 43 days after onset) were acute and convalescent specimens from patients with a positive anti-WNV IgM test (ELISA; Focus Diagnostics, Cypress, CA). Group III consisted of 43 patient sera collected between 6 and 12 months after infection. IgG antibodies specific for WNV were detected in 38% (ELISA) and 50% (IIFT) of group I sera, in 90% (ELISA and IIFT) of group II sera, and in 100% (ELISA and IIFT) of group III sera. Low-avidity IgG antibodies were demonstrated in 86% (ELISA) and 95% (IIFT) of IgG-positive patient samples taken between 2 and 43 days after the onset of symptoms (groups I and II). High-avidity IgG antibodies were detected in 100% of group III sera obtained 6 months or more after the onset of symptoms (ELISA and IIFT). IgG avidity tests for WNV infections are rapid and simple to perform. The determination of IgG avidity provides additional diagnostic certainty in differentiating between recently acquired and previous infections with WNV.

Seroprevalence of HSV-1 and HSV-2 in Barbados

Type-specific enzyme-linked immunosorbent assays, based upon recombinant glycoprotein G (gG), were used to detect antibodies to HSV-1 and HSV-2, in a small Caribbean island population. A blinded serosurvey was performed on samples from 184 blood donors, 122 pregnant women, and 120 HIV-positive patients. The seroprevalence of HSV-1 and HSV-2 was 81% and 34%, respectively, in blood donors, 84% and 40% in the antenatal population and 89% and 77% in the HIV-positive group. As expected the majority of adults were seropositive against HSV-1. However, the HSV-2 seroprevalence was significantly higher in HIV-infected adults than in the other groups. These findings support the need for prospective epidemiological studies in this population.

Reclassification of Leptospira parva Hovind-Hougen et al. 1982 as Turneriella parva gen. nov., comb. nov

Analysis of the G+C content, DNA–DNA relatedness to other leptospires and 16S rRNA gene sequence of Leptospira parva showed that this species was not related to other Leptospira species. On the basis of these data, it is proposed that Leptospira parva should be transferred to the genus Turneriella as Turneriella parva gen. nov., comb. nov., with strain HT (=NCTC 11395T=ATCC BAA-1111T) as the type strain.

A prospective study of asymptomatic Chlamydia trachomatis in Barbadian women

A prospective study to determine the prevalence of asymptomatic female genital tract Chlamydia trachomatis infection was performed on 167 women at the Queen Elizabeth Hospital, Barbados, West Indies and at a private clinic. The ELISA (Microtrak, chlamydia EIA, Syva, CA) method was used to detect Chlamydia trachomatis antigen. Nineteen (11.4% 95% CI 6.5-16.3) women were found positive. The efficacy of a single 1 gram dose of azithromycin given orally to 18 patients was tested after 4 weeks. One patient who was pregnant was given 500 mg erythromycin four times daily orally for 1 week. Only six patients (including the pregnant patient) reported for follow up. All six repeat swabs were negative for C. trachomatis antigen. The prevalence of 11.4% asymptomatic chlamydial infection in endocervical swabs in Barbadian women is in agreement with a previous study which reported a prevalence of 18.4% +/7.8%. Patient compliance was assured, using a single dose of azithromycin. It was found to be as effective as doxycyline and ciprofloxacin as reported by other workers.

Human external ophthalmomyiasis occurring in Barbados

Human infection with the sheep nasal botfly Oestrus ovis occurs sporadically. In most cases, there is a history of a strike in the eye by the adult fly. Human O. ovis has been reported rarely from the Americas. We report the first case of O. ovis infection in the Caribbean region, which occurred in an urban area of Barbados. The patient responded to removal of the larvae from the conjunctiva and symptomatic treatment.

Persistence of anti-leptospiral IgM, IgG and agglutinating antibodies in patients presenting with acute febrile illness in Barbados 1979-1989

The persistence of anti-leptospiral IgM and IgG antibodies and agglutinating antibodies was studied in serologically confirmed cases of severe leptospirosis during the acute illness and over periods of several years after recovery. The antibody response in non-leptospirosis patients presenting to hospital with similar symptoms over the same period of time was used to estimate the background antibody level to leptospirosis in the community. All patients enrolled in the study had blood samples collected twice in the acute stage of illness, once during convalescence and then annually from the time of initial hospitalisation until the end of the study period. Six hundred and thirty-eight patients presented to hospital with acute febrile illness, of whom 321 were diagnosed with leptospirosis. Patients who had severe leptospirosis commonly remained seropositive, with IgM, IgG and agglutinating antibodies detectable for several years after infection. A significant proportion of cases had high titres of agglutinating antibody detectable by the microscopic agglutination test (> or = 800). There were marked differences in the magnitude and duration of persistence of agglutinating antibodies directed against different serogroups. More than 20% of cases with evidence of infection with serogroup Autumnalis retained titres of >800, 4 years after the acute illness. In one case a titre of 800 was detected 11 years after infection. Persistence of agglutinating antibody titres can create problems in interpretation of serological results and make it impossible to estimate the time of infection, given a specific titre. This study demonstrates that in endemic areas where seroprevalence is high, use of a single elevated titre is not reliable to define a current infection.

Leptospiral carriage by mice and mongooses on the island of Barbados

Leptospirosis is a zoonotic disease, maintained by chronic infection of the kidneys of reservoir animals, usually small mammals. Infection in humans is acquired from direct or indirect exposure to the urine of infected animals. Leptospirosis has a high incidence in tropical regions, and has been studied extensively in several Caribbean countries. We studied the carriage of Leptospira serovars by two small mammals which are potential maintenance hosts of the disease in Barbados. A total of 136 mongooses (Herpestes auropunctatus) and 97 mice (Mus musculus) were caught in live traps. Leptospiral antibodies were detected by microscopic agglutination test (MAT) using antigens representing 12 serogroups, and kidney tissues were inoculated into polysorbate medium for isolation of leptospires. The seroprevalence (at a titre of > or = 100) in mice was 28.2% (24/85, 95% CI 19.0, 39.1) and in mongooses 40.7% (48/118, 95% CI 31.7, 50.1). In mice, antibodies were detected predominantly against serogroups Ballum and Autumnalis, while in mongooses the predominant serogroup was Autumnalis. Leptospires were isolated from 28 mice (28.9%, 95% CI 20.1, 39.0) and from 4 mongooses (2.9%, 95% CI 0.8, 7.4). Mouse isolates were identified as serovars arborea (17) and bim (7). As in other parts of the world, common house mice (Mus musculus) represent a significant reservoir of leptospirosis. Although carriage of the Ballum serovar, arborea, was not unexpected, this represents the first time that an animal reservoir of serovar bim has been identified. This is significant because bim causes about 63% of human leptospirosis in Barbados, and control efforts and education for prevention can now be targeted at a specific reservoir.

Leptospiral proteins recognized during the humoral immune response to leptospirosis in humans

Leptospirosis is an emerging zoonosis caused by pathogenic spirochetes belonging to the genus Leptospira. An understanding of leptospiral protein expression regulation is needed to develop new immunoprotective and serodiagnostic strategies. We used the humoral immune response during human leptospirosis as a reporter of protein antigens expressed during infection. Qualitative and quantitative immunoblot analysis was performed using sera from 105 patients from Brazil and Barbados. Sera from patients with other diseases and healthy individuals were evaluated as controls. Seven proteins, p76, p62, p48, p45, p41, p37, and p32, were identified as targets of the humoral response during natural infection. In both acute and convalescent phases of illness, antibodies to lipopolysaccharide were predominantly immunoglobulin M (IgM) while antibodies to proteins were exclusively IgG. Anti-p32 reactivity had the greatest sensitivity and specificity: positive reactions were observed in 37 and 84% of acute- and convalescent-phase sera, respectively, while only 5% of community control individuals demonstrated positive reactions. Six immunodominant antigens were expressed by all pathogenic leptospiral strains tested; only p37 was inconsistently expressed. Two-dimensional immunoblots identified four of the seven infection-associated antigens as being previously characterized proteins: LipL32 (the major outer membrane lipoprotein), LipL41 (a surface-exposed outer membrane lipoprotein), and heat shock proteins GroEL and DnaK. Fractionation studies demonstrated LipL32 and LipL41 reactivity in the outer membrane fraction and GroEL and DnaK in the cytoplasmic fraction, while p37 appeared to be a soluble periplasmic protein. Most of the other immunodominant proteins, including p48 and p45, were localized to the inner membrane. These findings indicate that leptospiral proteins recognized during natural infection are potentially useful for serodiagnosis and may serve as targets for vaccine design.

Antimicrobial sensitivity of Haemophilus influenzae isolates from bacterial conjunctivitis

Haemophilus influenzae is one of the common bacterial pathogens which affect children. Resistance to frequently used antibiotics is becoming a significant problem in community isolates of common pathogens. A retrospective review was conducted of the serotypes and antimicrobial sensitivity of H influenzae isolates from bacterial conjunctivitis, over an 18-month period. Data on antimicrobial sensitivity (obtained by the National Committee for Clinical Laboratory Standards disk diffusion method) and beta-lactamase production, and typing results, were analysed. Ninety-nine isolates were recovered, of which 87 were typed. Most isolates were recovered from children under one year of age. Ninety-three percent were unencapsulated and biotypes I and IV were most common. H influenzae type b was recovered only twice. beta-lactamase was produced by 41% isolates while four isolates were ampicillin-resistant but did not produce beta-lactamase. All isolates were sensitive to chloramphenicol and 45% were co-trimoxazole sensitive. H influenzae is commonly isolated from bacterial conjunctivitis in Barbados and, as elsewhere, the majority of isolates are from small children and are non-encapsulated. However, there is a high prevalence of beta-lactamase production, which may serve as a reservoir for transfer to more invasive encapsulated strains of H influenzae within the oropharyngeal flora.

Leptospirosis

Leptospirosis is a worldwide zoonotic infection with a much greater incidence in tropical regions and has now been identified as one of the emerging infectious diseases. The epidemiology of leptospirosis has been modified by changes in animal husbandry, climate, and human behavior. Resurgent interest in leptospirosis has resulted from large outbreaks that have received significant publicity. The development of simpler, rapid assays for diagnosis has been based largely on the recognition that early initiation of antibiotic therapy is important in acute disease but also on the need for assays which can be used more widely. In this review, the complex taxonomy of leptospires, previously based on serology and recently modified by a genotypic classification, is discussed, and the clinical and epidemiological value of molecular diagnosis and typing is also evaluated.

Antibiotic susceptibility of Clostridium difficile isolates from adult patients at two Jamaican hospitals. Clinical and epidemiological implications

The susceptibility of 39 toxin producing Clostridium difficile isolates from stools of hospitalized patients was determined, by disc diffusion, to six antibiotics. All but one isolate (toxin A negative) produced toxin A and toxin B. A wide variation in susceptibility to clindamycin, tetracycline and chloramphenicol was noted. Erythromycin and cotrimoxazole showed a clear-cut discrimination in resistance and susceptibility, while all isolates were sensitive to vancomycin. Erythromycin sensitive isolates demonstrated a significant association with diarrhoea (60.9%, 14/23, p < 0.001). These strains were predominantly found at the University Hospital of the West Indies (UHWI, 94.1%, 16/17). Strains resistant to erythromycin and clindamycin together were commonly found at the National Chest Hospital (NCH, 68.2%, 15/22). All erythromycin sensitive strains found at the NCH were from patients transferred to that hospital. These findings suggest that there is a common strain of C difficile (erythromycin resistant) at the NCH different from that found at the UHWI; the resistant pattern seen with isolates from the NCH was typical of toxigenic serogroup C strain and could be typed by the the disc diffusion method. Patients at the NCH who were colonized with either of the two strains of C difficile were likely to get diarrhoea, once there was suppression of the normal microflora by antibiotics and colonic overgrowth with C difficile.

Two methods for rapid serological diagnosis of acute leptospirosis

Leptospirosis is a common and underdiagnosed zoonosis. Two rapid assays for serological diagnosis of acute leptospirosis in diagnostic laboratories, the immunoglobulin M (IgM)-dipstick assay and the indirect hemagglutination assay (IHA), were evaluated and compared with standard assays. Sera were examined from 104 patients admitted to a hospital for investigation in a leptospirosis diagnostic protocol. Specimens for serology were taken on days 1 and 4 of the patients' hospital stay. Antibodies were detected using an IgM-enzyme-linked immunosorbent assay (ELISA), microscopic agglutination test (MAT), an IgM-dipstick assay, and an IHA. Fifty-one patients were found to have leptospirosis. The sensitivity of the IgM-dipstick assay was 98%, its specificity was 90.6%, its positive predictive value was 90.9%, and its negative predictive value was 98%. The sensitivity of the IHA was 92.2%, its specificity was 94.4%, its positive predictive value was 95.9%, and its negative predictive value was 92.7%. The standard IgM-ELISA and MAT, were positive in the first samples tested from 67 and 55% of the cases, respectively, and the rapid IgM-dipstick assay and IHA were positive in 71 and 49%, respectively, in the first sample tested. Both rapid assays are highly sensitive and specific. Neither requires specialized equipment, and both are suitable for use in diagnostic laboratories.

Testing for gene-gene interaction controlling total IgE in families from Barbados: evidence of sensitivity regarding linkage heterogeneity among families

Genetic heterogeneity has been proposed as a hallmark feature of allergic disease. To test the hypothesis that total IgE levels are jointly influenced by a locus on chromosome 12q21.1-q21.31 and a locus on 17q11.2-q21.2, we conducted multipoint allele-sharing analyses using nonparametric linkage (NPL) methods on Afro-Caribbean families from Barbados to test for evidence of gene-gene interactions. Significant correlations were observed between NPL scores at D12S1052 and both D17S1293 and D17S1299 for a dichotomized phenotype of total IgE. An analysis of family-specific NPL scores revealed that evidence for interaction was being driven largely by one multiplex pedigree (NPL = 12.01, 12.23, and 12.16 at D12S1052, D17S1293, and D17S1299, respectively). Using the programs SIMWALK (v2.0) and GOLD, a different set of haplotypes in this influential family was observed around D12S1052 and the 17q loci compared to the other Barbados pedigrees. Our findings are a classic example of founder effect, provide evidence for sensitivity of this type of linkage analysis to unusual pedigrees, and highlight an element of genetic heterogeneity that has been given little attention in the study of complex traits.

Leptospirosis occurring in two children after fresh water immersion

Leptospirosis is relatively uncommon in children. Two cases of severe leptospirosis occurred in teenaged boys who shared a common exposure via immersion in fresh water. While both patients had laboratory-confirmed leptospirosis, their symptoms differed in many respects.

The leptospiral major outer membrane protein LipL32 is a lipoprotein expressed during mammalian infection

We report the cloning of the gene encoding the 32-kDa lipoprotein, designated LipL32, the most prominent protein in the leptospiral protein profile. We obtained the N-terminal amino acid sequence of a staphylococcal V8 proteolytic-digest fragment to design an oligonucleotide probe. A Lambda-Zap II library containing EcoRI fragments of Leptospira kirschneri DNA was screened, and a 5.0-kb DNA fragment which contained the entire structural lipL32 gene was identified. Several lines of evidence indicate that LipL32 is lipid modified in a manner similar to that of other procaryotic lipoproteins. The deduced amino acid sequence of LipL32 would encode a 272-amino-acid polypeptide with a 19-amino-acid signal peptide, followed by a lipoprotein signal peptidase cleavage site. LipL32 is intrinsically labeled during incubation of L. kirschneri in media containing [(3)H]palmitate. The linkage of palmitate and the amino-terminal cysteine of LipL32 is acid labile. LipL32 is completely solubilized by Triton X-114 extraction of L. kirschneri; phase separation results in partitioning of LipL32 exclusively into the hydrophobic, detergent phase, indicating that it is a component of the leptospiral outer membrane. CaCl(2) (20 mM) must be present during phase separation for recovery of LipL32. LipL32 is expressed not only during cultivation but also during mammalian infection. Immunohistochemistry demonstrated intense LipL32 reactivity with L. kirschneri infecting proximal tubules of hamster kidneys. LipL32 is also a prominent immunogen during human leptospirosis. The sequence and expression of LipL32 is highly conserved among pathogenic Leptospira species. These findings indicate that LipL32 may be important in the pathogenesis, diagnosis, and prevention of leptospirosis.

Atopic dermatitis is associated with a functional mutation in the promoter of the C-C chemokine RANTES

Up-regulation of C-C chemokine expression characterizes allergic inflammation and atopic diseases. A functional mutation in the proximal promoter of the RANTES gene has been identified, which results in a new consensus binding site for the GATA transcription factor family. A higher frequency of this allele was observed in individuals of African descent compared with Caucasian subjects (p < 0.00001). The mutant allele was associated with atopic dermatitis in children of the German Multicenter Allergy Study (MAS-90; p < 0.037), but not with asthma. Transient transfections of the human mast cell line HMC-1 and the T cell line Jurkat with reporter vectors driven by either the mutant or wild-type RANTES promoter showed an up to 8-fold higher constitutive transcriptional activity of the mutant promoter. This is the first report to our knowledge of a functional mutation in a chemokine gene promoter. Our findings suggest that the mutation contributes to the development of atopic dermatitis. Its potential role in other inflammatory and infectious disorders, particularly among individuals of African ancestry, remains to be determined.

Detection of dengue infection in patients investigated for leptospirosis in Barbados

The annual incidence of leptospirosis in Barbados is approximately 13 severe cases/100,000. The peak incidence occurs in October to December of each year, coinciding with the months of heaviest rainfall. During the second half of 1995, an epidemic of dengue type 1 infection produced almost 1,000 laboratory-confirmed cases. During the same period, leptospirosis mortality was twice the average, suggesting that some cases of leptospirosis were being misdiagnosed and treated inappropriately. Sera from patients investigated for dengue or leptospirosis were analyzed retrospectively to determine the extent of misdiagnosis. During 1995 and 1996, 31 of 139 and 29 of 93 patients, respectively, were confirmed as having leptospirosis. Sera from the remaining leptospirosis-negative patients were tested for IgM antibodies to dengue virus. During 1995 and 1996, 48 of 108 patients and 21 of 64 patients, respectively, were found to have dengue. In 1997, sera from all patients investigated for leptospirosis were also tested prospectively for IgM antibodies to dengue: 38 of 92 leptospirosis-negative patients (41%) were dengue IgM-positive, while 2 of 25 leptospirosis cases also had serologic evidence suggesting acute dengue infection. A second large outbreak of dengue caused by serotype 2 occurred in 1997. During the 1995 and 1997 dengue epidemics in Barbados, dengue cases outnumbered leptospirosis cases investigated in the leptospirosis diagnostic protocol. During 1997, patients investigated but negative for dengue were also tested for anti-leptospiral IgM: 7.3% (19 of 262) were IgM-positive. Substantial misdiagnosis of both dengue and leptospirosis can occur and greater public awareness and clinical suspicion of the similar presentations of these two diseases are necessary.

Assessment of the efficacy of an IgM-elisa and microscopic agglutination test (MAT) in the diagnosis of acute leptospirosis

In a prospective study in Barbados between 1979 and 1989, 321 cases were diagnosed in 638 patients presenting at a hospital with symptoms of leptospirosis. Initial diagnosis was based on patient history and characteristic signs and symptoms. In 92 cases (29%), diagnosis was confirmed by isolation of organisms from the blood, urine, or dialysate fluid; in the remaining 229 cases (71%) diagnosis was confirmed by serology alone. Results of an IgM-ELISA and microscopic agglutination test (MAT) in cases with isolates and in non-leptospirosis cases were used to assess the sensitivity and specificity of the tests. The sensitivity of IgM detection by ELISA was 52% in the first acute-phase specimen, increasing to 89% and 93% in the second acute-phase and convalescent specimens, respectively. The specificity of the IgM-ELISA was high (> or = 94%) in all specimens. The sensitivity of the MAT was low (30%) in the first acute-phase specimen, increasing to 63% in the second acute-phase specimen and 76% in the convalescent specimen. The specificity of the MAT was > or = 97% in all specimens.

International multicenter evaluation of the clinical utility of a dipstick assay for detection of Leptospira-specific immunoglobulin M antibodies in human serum specimens

We performed a multicenter evaluation of a robust and easily performed dipstick assay for the serodiagnosis of human leptospirosis. The assay is aimed at the detection of Leptospira-specific immunoglobulin M (IgM) antibodies. The study involved 2,665 serum samples collected from 2,057 patients with suspected leptospirosis in 12 countries on five continents with different levels of endemicity and different surveillance systems. The patients were grouped as laboratory-confirmed leptospirosis case patients and noncase patients based on the results of culturing and the microscopic agglutination test. Paired samples from 27.7% of the subjects were tested. Of the 485 case patients, 87.4% had a positive dipstick result for one or more samples. Of the 1,513 noncase patients, only 7.2% had a positive result. Whereas most (88.4%) of the positive samples from the case patients showed moderate to strong (2+ to 4+) staining in the dipstick assay, most (68.1%) of the positive samples from the noncase patients showed weak (1+) staining. The sensitivity of the dipstick assay increased from 60.1% for acute-phase serum samples to 87.4% for convalescent-phase samples. The specificities for these two groups of samples were 94.1 and 92.7%, respectively. The dipstick assay detected a broad variety of serogroups. The results of the dipstick assay were concordant (observed agreement, 93.2%; kappa value, 0.76) with the results of an enzyme-linked immunosorbent assay for the detection of specific IgM antibodies, a test which is often used in the laboratory diagnosis of current or recent leptospirosis. This study demonstrated that this easily performed dipstick assay is a valuable and useful test for the quick screening for leptospirosis; has a wide applicability in different countries with different degrees of endemicity; can be used at all levels of the health care system, including the field; and will be useful for detecting and monitoring outbreaks of leptospirosis.

Dense mapping of chromosome 12q13.12-q23.3 and linkage to asthma and atopy

BACKGROUND

Asthma is a complex disease characterized by a high prevalence of allergic diathesis and the almost ubiquitous presence of upper airway disease (eg, rhinitis). Previously, we observed linkage of asthma among Afro-Caribbean families to markers in chromosome 12q, which contains a number of genes encoding for products closely related to allergic airway inflammation and disease.

OBJECTIVE

To identify susceptibility loci in chromosome 12q contributing to the genetics of upper and lower airway diseases and to expand the region to include genes encoding IFN-gamma (IFNG ) and one of the signal transducers and activators of transcription (STAT6 ), we conducted further linkage studies among 33 multiplex families.

METHODS

We characterized 528 subjects from Barbados for asthma; 82% were characterized for allergic rhinitis. Two-point and multipoint linkage analysis of 22 microsatellite markers (spanning approximately 79 centimorgan) was performed.

RESULTS

Affected sib-pair analysis revealed significant evidence for linkage to asthma over approximately 30 cM (P <.05 to.002), with the best evidence for linkage at a CA repeat polymorphism in the first intron of IFNG in 12q21.1 (P =.002). Evidence of linkage to allergic rhinitis was observed in the same region (D12S313, P = 0.006, and IFNGCA, P =.01, respectively). Multipoint linkage analysis also provided evidence for linkage to asthma, with the best nonparametric linkage analysis score at D12S326 (nonparametric linkage score = 3.8, P =.0008). Modest evidence for linkage to allergic rhinitis was observed next to D12S326 at D12S1052 (P =.036).

CONCLUSIONS

Our findings suggest that (1) one or more loci in the chromosome 12q13. 12-q23.3 region are contributing to the expression of the clinical phenotype asthma and the strongest evidence for linkage is in a region near the gene encoding IFNG and (2) a susceptibility locus for both asthma and allergic rhinitis maps to this region.

Evaluation of four methods for detection of immunoglobulin M antibodies to dengue virus

Dengue has become hyperendemic in many islands of the Caribbean region. The performance in a diagnostic laboratory of four commercial assays for detection of immunoglobulin M (IgM) antibodies was evaluated. Sera from 62 patients with dengue virus infection were studied. These included 18 patients from whom dengue virus type 2 was isolated in a 1997 outbreak (specimens collected a mean of 14 days after onset of symptoms), 8 patients with dengue hemorrhagic fever (mean time after onset, 11 days), and 36 patients in whom dengue was previously confirmed by serology (mean time after onset, 10 days). Thirty serum specimens from blood donors in a country where dengue is not endemic were used as negative controls. The methods evaluated were two IgM-capture enzyme-linked immunosorbent assays (ELISA) (MRL Diagnostics, Cypress, Calif., and PanBio, Queensland, Australia), a dot ELISA dipstick assay (Integrated Diagnostics, Baltimore, Md.), and a rapid immunochromatographic assay for dengue IgG and IgM (PanBio IC). IgG antibodies were also detected by an ELISA method (MRL Diagnostics). The sensitivities of the four assays were as follows: MRL Diagnostics IgM ELISA, 98.4%; PanBio IgM ELISA, 85.5%; Integrated Diagnostics IgM dot ELISA, 96. 8%; and PanBio IC, 83.9%. The specificities of all tests were 100%. Evidence of secondary dengue was found in all patients with dengue hemorrhagic fever and in 83% of the remaining patients. The MRL Diagnostics IgM ELISA appears to be more sensitive than the PanBio IgM ELISA, and this may be significant when IgM titers are low, particularly in patients with secondary dengue infections. The dot ELISA dipstick assay is equally sensitive and may be more appropriate for use in laboratories with lower workloads.

Clustering of cases of Mycobacterium fortuitum infection investigated by molecular typing

Organisms of the Mycobacterium fortuitum complex are recognised but uncommon causes of pulmonary disease, primary cutaneous disease and a wide spectrum of nosocomial infections. M fortuitum was isolated from 20 patients over a 15 month period, with an apparent clustering of isolates occurring from January to March 1994. The molecular epidemiology of this clustering was investigated using an arbitrary primer polymerase chain reaction method (AP-PCR). 21 isolates were studied, which yielded 13 distinct profiles. Multiple isolates from a single patient yielded identical profiles. All of seven isolates recovered during the six week period from January to March 1994 shared a common profile which was distinct from all other isolates, suggesting that a single strain was isolated from specimens from all seven patients. The source of this cluster is uncertain. We can find no epidemiological basis for an episode of cross-infection within the hospital environment, and it is assumed that contamination of the specimens during collection, transport or processing was responsible for the "pseudo-outbreak" of M fortuitum.

Surveillance of leptospiral carriage by feral rats in Barbados

Rodents, particularly rats, are widely held to be the source of most human cases of leptospirosis. Feral rats were trapped at sites throughout Barbados during two six month surveys: from October to March 1986/87 and from October to March 1994/95. During the first survey, 63 rats were trapped, of which 26 (41%) were identified as Rattus rattus and 37 (59%) as Rattus norvegicus. In the second study, 100 rats were trapped, of which R. rattus comprised 24% (24) and R. norvegicus 76% (76). Cultures of blood, urine and kidney were made in EMJH medium. Leptospires were isolated from 12/63 (19%) and from 16/100 (16%) of the rats during 1986/87 and 1994/95, respectively; 27/28 isolates were recovered from the kidneys or urine or both, while only one isolate was recovered from the blood. During the first study, isolates were identified as serovars copenhageni (11) and arborea (1), while in the second study, serovars copenhageni (9), arborea (5) and bim (1) were identified; one isolate was lost before it could be identified. In the first study, antibodies were detected by microscopic agglutination at a titre of > or = 100 in 26/62 (42%) of rats tested, while in the second survey, 5/100 (5%) of rats had similar titres. In two surveys, conducted eight years apart, we confirmed that rats in Barbados are commonly infected with leptospires, and that viable organisms are found in the kidneys and urine, evidence of chronic infection and thus excretion of leptospires in rodent urine. Moreover, the predominant serovar isolated was copenhageni, of which Rattus spp. are the worldwide reservoir. There was little evidence that rats act as a reservoir for the serovar bim, the most common cause of human leptospirosis in Barbados.

Evaluation of the indirect hemagglutination assay for diagnosis of acute leptospirosis

Serology plays an important role in the diagnosis of leptospirosis. Few laboratories have the resources and expertise to perform the microscopic agglutination test. There is a need for rapid and simple serological tests which facilitate the early diagnosis of leptospirosis, while antibiotic therapy may be most effective. A commercially available indirect hemagglutination assay (IHA; MRL Diagnostics, Cypress, Calif.) was evaluated with multiple serum specimens from 107 patients being investigated for leptospirosis. By using a combination of enzyme-linked immunosorbent assay (ELISA) methods for immunoglobulin M (IgM) and IgG antibodies and the microscopic agglutination test, 54 patients were found to have leptospirosis and 53 were found not to have leptospirosis. The sensitivity of IHA for the detection of acute leptospirosis was 100%, the specificity was 94%, the positive predictive value was 95%, and the negative predictive value was 100%. IHA was negative when 13 antinuclear antibody-positive sera, 24 serum specimens from patients with syphilis, and 16 serum specimens false positive by the Venereal Disease Research Laboratory test were tested. IHA was shown to detect both IgM and IgG classes of antibodies in human sera. Serum specimens from 27 dogs investigated for leptospirosis were studied: 3 samples gave nonspecific hemagglutination, but for all remaining samples, the results of IHA and an IgM ELISA were concordant. Performance of IHA was simple, and IHA requires no specialized equipment. It represents a useful assay for laboratories which require a leptospiral diagnostic capability but lack the expertise to perform specialist investigations.

Seroepidemiology of canine leptospirosis on the island of Barbados

Previous surveillance in Barbados documented the absence of infection with Leptospira serogroup Canicola in dogs. The aim of this study was to survey the current state of canine leptospirosis in Barbados, 10 years after the last survey. Sera from 78 unwanted dogs scheduled for euthanasia and 61 dogs suspected of having acute leptospirosis were tested by microscopic agglutination (MAT) and by an ELISA method adapted for canine IgM and IgG antibodies. The seroprevalence in unwanted dogs was 62% (48/78), at an MAT titre of > or = 100. The majority of animals had low titres, suggestive of previous infection. Serogroup Autumnalis was the most common reactor (45%), followed by serogroups Icterohaemorrhagiae and Australis (each 16%) and Pomona (13%). Serogroup Ballum was uncommon in this group. The seroprevalence determined by MAT in acutely-ill dogs was 75% (46/61). The most common predominant serogroup was Icterohaemorrhagiae (36%) followed by serogroup Australis (13%), while serogroups Autumnalis and Ballum were also of little significance. Paired specimens were available from eight acutely-ill dogs. One animal was seronegative while five dogs showed evidence of seroconversion. An IgM-ELISA titre of > or = 320 was used to confirm current infection in eight of these nine animals. Previous studies in Barbados showed a higher prevalence of serogroup Icterohaemorrhagiae than of Autumnalis, but the relative frequency of these two serogroups may be changing. The high seroprevalence in dogs is of public health concern because the close contact between dogs and man may provide the link between a reservoir in the environment and susceptible humans.

Penicillin-resistant Streptococcus pneumoniae isolated in Barbados

An imported case of pneumonia caused by penicillin-resistant Streptococcus pneumoniae occurred in a tourist, shortly after arriving in Barbados. The isolate was of serogroup 6 and exhibited intermediate resistance to penicillin. This was the first isolation of penicillin-resistant S. pneumoniae in Barbados.

Severe primary HIV-1 infection among black persons in Barbados

Descriptions of primary HIV-1 infection have so far been based on Caucasians living in industrialized nations. Due to studies of leptospirosis in the predominantly black population of Barbados, serum was available for patients admitted with acute febrile illnesses to the Queen Elizabeth Hospital (QEH). By searching the medical records of 510 adult patients with known HIV-1 infection we identified 10 patients who had stored serum from an admission for an acute febrile illness that predated or coincided with their first HIV-1-positive test. Serological testing confirmed primary HIV-1 infection in 9 and was suggestive in the 10th patient. The clinical features of these 10 patients were in keeping with previous descriptions of primary HIV-1 infection but differed from leptospirosis cases seen at the QEH. One patient died during his seroconversion illness and another died 3 months after seroconversion. The findings suggest that severe primary HIV-1 infection could be a relatively uncommon occurrence, that the condition may be misdiagnosed, and that cases may not occur until the AIDS epidemic is established.

Epidemiology of Helicobacter pylori infection in Barbados

The epidemiology of Helicobacter pylori infection in Barbadian patients and controls was studied. H. pylori was isolated from biopsies from 50/100 (50%) adult patients undergoing endoscopy for investigation of upper gastrointestinal tract symptoms. Urease was detected in biopsies from 54 patients and gastritis was detected by histology in 71 patients. Serology was performed using a commercial ELISA method. Using an IgG concentration of 10 U/ml as a threshold, antibodies were detected in 78% of 100 patients undergoing endoscopy, 72% of 230 blood donors and 22% of 50 children. The mean antibody concentration was significantly higher in patients (92 U/ml) than in blood donors (49 U/ml) or in children (9.5 U/ml). Culture-positive patients (120 U/ml) had higher IgG concentrations than culture-negative patients (64 U/ml). Using isolation of H. pylori or a positive biopsy urease test as a measure of true prevalence of infection, the sensitivity of serology was 96%, the specificity 42%, positive predictive value 67% and negative predictive value 90%. Seroprevalence increased with age, to a peak of more than 90% in blood donors aged 50-59 years and in patients aged over 60 years. The epidemiology of H. pylori in Barbados is similar to that in developed countries, where few children are infected, but resembles other developing countries in the high seroprevalence observed in middle-aged adults. Our results confirm the utility of serology for detecting H. pylori by a non-invasive technique.

Differentiation of Leptospira species and serovars by PCR-restriction endonuclease analysis, arbitrarily primed PCR and low-stringency PCR

Reference strains from 30 serovars representing seven species of Leptospira and 48 recent isolates from human patients, dogs and rats, were characterised by polymerase chain reaction-restriction endonuclease analysis (PCR-REA), arbitrarily primed PCR (AP-PCR) and low stringency PCR (LS-PCR). PCR-REA analysis yielded seven groups among 29 serovars of pathogenic Leptospira; the non-pathogenic L. biflexa serovar patoc was not amplified with the primer pairs studied. AP-PCR and LS-PCR fingerprinting resulted in 25 and 21 distinct profiles, respectively, among the 30 reference strains. The results of the three PCR-based techniques were highly concordant and were in general agreement with those from previous DNA studies, confirming the high level of polymorphism among Leptospira species and serovars, and supported the concept of the serovar as the basic taxonomic unit of leptospiral classification. Results of the PCR-based typing methods for 11 randomised leptospiral strains, 36 clinical isolates from human patients and dogs and 12 survey isolates from trapped rats agreed with those from serological identification. With one exception, isolates of the same serovar gave identical profiles irrespective of the source. AP-PCR and LS-PCR are simple to perform and interpret, and appear to be useful for characterising isolates of Leptospira spp. for diagnostic and epidemiological purposes.

Linkage of asthma and total serum IgE concentration to markers on chromosome 12q: evidence from Afro-Caribbean and Caucasian populations

To identify genes potentially relevant in atopic asthma, we analyzed markers in chromosome 12q15-q24.1 for linkage to asthma and total serum IgE concentration. Sib-pair analyses of 10 markers in 345 full- and 219 half-sib pairs from 29 multiplex Afro-Caribbean families provided evidence for linkage to this region for both asthma and total serum IgE. Certain alleles at these loci showed significant evidence of transmission disequilibrium with both asthma and high IgE. Using 6 of these markers and 11 additional markers, evidence for linkage of total IgE to 12q was also found in 12 Caucasian Amish kindreds (24 nuclear families) by both sib-pair and transmission disequilibrium analyses. These findings suggest that the 12q15-q24.1 region may contain a gene(s) controlling asthma and the associated "high total IgE" trait.

Serological survey of leptospirosis in livestock animals in the Lesser Antilles

A serological survey was performed of 1788 cattle, goats and sheep on 13 islands in the Lesser Antilles. Sera were tested by microscopic agglutination (MAT) using a panel of 22 live antigens. Evidence of past exposure, at a titer of > or = 100, was found in 101 animals (5.6%). Antibodies were more common in cattle and goats (7.2% in each) than in sheep (1.7%). Seroprevalence was highest in cattle in Martinique (20%) and in goats in St. Vincent (23%). The predominant serogroups were Sejroe (largely confined to cattle in Martinique), Autumnalis, Icterohaemorrhagiae, Grippotyphosa, and Cynopteri. Eleven cattle from Martinique and 2 sheep with titers of > or = 800 showed evidence of recent infection.

Longitudinal study of molecular epidemiology of small round-structured viruses in a pediatric population

Small round-structured viruses (SRSV), recently designated members of the family Caliciviridae, can now be readily subtyped by amplification of a defined portion of their genome by reverse transcription-PCR and then by identification of the amplicons with specific probes by Southern blotting. A longitudinal survey (from 1991 to 1995) was conducted to determine the genotypes of the SRSV present in pediatric stool specimens from patients with sporadic cases of gastroenteritis. It was found that almost all viruses were of the G-2 genotype, and on probing, the subtype P2-B was predominant but the frequencies of the different subtypes varied from year to year. A survey of the genotypes of SRSV from community outbreaks from 1995 showed that the G-2 genotype was also predominant and that the distribution of its subtypes was similar to that seen in sporadic cases of diarrhea in pediatric patients over the same time period. It was concluded that there is a succession of subtypes of SRSV in our pediatric population over time. This distribution of genotypes in sporadic cases of pediatric gastroenteritis may reflect the distribution in community outbreaks occurring at the same time.

Antibiotic sensitivity of Neisseria gonorrhoeae isolates in Barbados: longitudinal surveillance 1990-1994

The antimicrobial susceptibility of 775 isolates of Neisseria gonorrhoeae, recovered in Barbados over a five-year period, was studied by disc diffusion. Sensitivity to penicillin declined from 56% in 1990 to 38% in 1994. The prevalence of beta-lactamase production rose from 30% to 50% during this period and sensitivity to tetracycline declined from 96% to 46%, while co-trimoxazole and spectinomycin sensitivities varied. Ceftriaxone, norfloxacin and erythromycin were the only compounds tested to which sensitivity remained uniform. The results confirm the current recommendations by several agencies that ceftriaxone or an oral fluoroquinolone should be considered the drug of choice for the empirical treatment of gonorrhoea.

Genital tract infections in sexually active women in Barbados

Ninety-eight women attending three different clinics were prospectively studied for the presence of genital tract infections, including Chlamydia trachomatis. Of these 98 women, 35 were presenting to a polyclinic with symptoms of genital tract infection, 55 were attending an antenatal clinic for their first visit, and 8 referred to a colposcopy clinic because of an abnormal Papanicolaou smear were included. Gonorrhoea was detected in one patient, syphilis in two, and Trichomonas vaginalis in six. Candida albicans and Chlamydia trachomatis were each detected in 18 patients, while the most common condition was bacterial vaginosis, detected in 35 patients. The prevalence of these infections was lowest in patients referred for colposcopy and highest in the women attending the antenatal clinic. Chlamydia trachomatis was the most common sexually-transmitted pathogen detected in this population. These data emphasise the need for an aggressive approach to the diagnosis and treatment of chlamydial infection in females.