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Biomedical subjects

A M Johnson

Publications and source records attributed to A M Johnson.

At least 145 records · Page 8Linked to original sources
PubMed1996

Spectrum of disease in Africans with AIDS in London.

OBJECTIVE: To compare the spectrum of disease, severity of immune deficiency and chemoprophylaxis prescribed in HIV-infected African and non-African patients in London. DESIGN: Retrospective review of case notes of all HIV-infected Africans and a comparison group of non-Africans attending 11 specialist HIV/AIDS Units in London. MAIN OUTCOME MEASURES: Comparison of demographic information, first and subsequent AIDS-defining conditions, levels of immune deficiency, and chemoprophylactic practices between the African and non-African groups. RESULTS: A total of 1056 Africans (313 developing AIDS) and 992 non-Africans (314 developing AIDS) were studied. Africans presented later than non-Africans (median CD4+ lymphocyte counts at diagnosis 238 and 371 x 10(6)/l, respectively). Tuberculosis accounted for 27% of initial episodes of AIDS in Africans and 5% in non-Africans; Pneumocystis carinii pneumonia (PCP) was the initial AIDS-defining condition in 34% of non-Africans and 17% of Africans. The incidence of tuberculosis in Africans with another AIDS-indicator disease was 16 per 100 person-years. PCP prophylaxis was prescribed for 40% Africans and 32% non-Africans; only 8% of Africans received tuberculosis preventive therapy. CONCLUSIONS: HIV-infected African patients presented at lower levels of CD4+ lymphocyte count, at a more advanced clinical stage, and with different AIDS-indicator diseases as compared with non-Africans. Prophylaxis against tuberculosis should be considered for all HIV-infected African patients in industrialized countries. The high incidence of diseases that are indicative of advanced immunodeficiency (e.g., cytomegalovirus disease) in African patients contrasts with data from Africa, suggesting better survival chances in the UK.

Acquired Immunodeficiency Syndrome↗
PubMed1996

Voluntary universal antenatal HIV testing.

OBJECTIVES: To assess the uptake of universal voluntary named HIV testing of hospital booked antenatal women and to identify behavioural and demographic factors associated with testing. To identify the number of previously undiagnosed women detected by the new policy and to compare prevalence among those testing with that measured by unlinked anonymous monitoring. DESIGN: Self-completion questionnaire and data abstraction from structured booking forms and virology laboratory records. SETTING: Central London teaching hospital antenatal clinic. PARTICIPANTS: One thousand three hundred and seventy-four women booking with a hospital based midwife during the 49 weeks from 27 July 1993 to 1 July 1994. RESULTS: Before the introduction of the new testing policy fewer than 10 women per year had an HIV test, and during the study this rose to 41% (548/1340). In univariate analysis, caucasian and Mediterranean ethnic origin, fewer previous live births, and more than one lifetime sexual partner were associated with higher uptake of HIV testing. In a multivariate model only the number of previous live births and ethnic origin remained significantly associated with testing. Six women out of 828 (1%) who completed the question about nonprescribed drug use stated that they had injected drugs, and four of these women accepted a test. Two women, both with recognised major risk factors for HIV infection, were diagnosed HIV antibody positive (a prevalence in the tested women of 0.36%). A further three women were already known to be HIV antibody positive. During the 12 months from July 1993 seven women (0.24%) were found to be positive by unlinked anonymous testing. CONCLUSIONS: The introduction of a universal approach to antenatal HIV testing appears feasible: it increased the uptake of the test and detected previously unrecognised infections. Many women chose not to be tested, however, and cases remained undiagnosed. Further studies are required to examine different models of offering HIV testing, reasons for declining the test, and the cost-benefit of antenatal HIV screening.

Adolescent↗
PubMed1996

A case control study of HIV seroconversion in gay men, 1988-1993: what are the current risk factors?

OBJECTIVE: To investigate current risk factors for HIV seroconversion among homo/bisexual men. DESIGN: Matched case control study in a large STD clinic in central London. Data on risk factors were obtained by case note review. METHODS: Fifty-six cases who had at least one negative HIV test followed by a positive test between June 1988 and July 1993, and two homo/bisexual controls (having two or more negative HIV tests) matched to each case on age, total number of HIV tests and test interval period were identified. Univariate and multivariate odds ratio were calculated for acute STD, ano-genital intercourse, condom use and HIV status of sexual partners. RESULTS: Adjusted odds ratios (95% confidence intervals) for HIV seroconversion were 4.1 (1.3-13.3) for having an acute interval STD and 4.6 (1.4-15.4) for having a known HIV infected sexual partner. Compared with men who always used condoms, odds ratios for men who sometimes or never used condoms were 7.9 (2.2-28.9) and 16.2 (3.0-86.0) respectively. Unprotected ano-genital intercourse was commonly reported by both cases and controls, and reported condom use was no greater with a known HIV infected partner than with a partner of unknown HIV status. CONCLUSION: HIV seroconversion among homo/bisexual men attending STD clinics is strongly related to having an acute STD, a known HIV infected partner and not using condoms. Although consistent use of condoms is highly protective, knowing that a partner is HIV infected does not ensure condom use between serodiscordant men. More effective, well-evaluated interventions are needed to reduce sexual risk-taking in this population.

Adolescent↗
PubMed1996

Who goes to sexually transmitted disease clinics? Results from a national population survey.

OBJECTIVES: To examine the pattern of attendance at sexually transmitted disease (STD) clinics in Britain. To compare the demographic characteristics, behaviours and attitudes of STD clinic attenders with those of non-attenders, and to assess the extent to which STD clinics are used by those with high-risk sexual lifestyles. DESIGN: Random sample general population survey of sexual attitudes and lifestyle. SUBJECTS: 18,876 randomly selected men and women resident in Britain aged 16-59 years. MAIN OUTCOME MEASURES: Demographic characteristics, pattern of homosexual partnerships, heterosexual partnerships, payment for sex, abortion, drug injection in the last five years, and attitudes to sexual behaviours amongst 512 respondents who had attended STD clinic in the last five years compared with those who had not. RESULTS: 8.3% of men and 5.6% of women had attended a clinic in their lifetime and 3.4% and 2.6% respectively in the last five years. Attendance rates varied substantially with area of residence. 11% of Inner London residents had attended in the last five years. In multivariate analysis, STD clinic attendance for men was most strongly associated with increased numbers of heterosexual partners, (OR = 6.01 (4.44-8.15) and homosexual partnerships (OR = 9.59 (5.83-15.8)) and more weakly associated with payment for sex, non-manual social class, age 25-44, unmarried status and smoking. Clinic attendance for women was most strongly associated with numbers of heterosexual partners (OR = 3.74 (2.76-5.08) and injecting drug use (OR = 4.39 (1.73-11.1)). A weaker independent association was found with a history of abortion, anal sex, non-manual social class, non-married status and age 16-24. From the total population, 1 in 6 men and 1 in 7 women in the top 5% of the distribution for numbers of heterosexual partners and 1 in 5 men paying for sex and 1 in 4 of those with a homosexual partner had attended a clinic in the last five years. The probability of attendance increased with multiple risk behaviours. Of women 64.2% and of men 69.7% attending clinics reported major risk markers for STD transmission. CONCLUSIONS: STD clinics in Britain are used by a wide demographic spectrum of the population. The behaviours, but not the attitudes, of attenders differed markedly from those of non-attenders. Clinics are relatively efficient in attracting only those with high-risk lifestyles, but, at a population level, the minority of those reporting risk-markers for STD transmission attend clinics. These findings suggest that STD clinics are an important focus for sexual health promotion, but that community programmes are also important for reaching non-attenders.

Adolescent↗
PubMed1996

Genetic studies in a black family with autosomal dominant polycystic kidney disease and sickle-cell trait.

Autosomal dominant polycystic kidney disease (ADPKD) is caused by at least two different genes. The ADPKD1 gene is located on chromosome 16p and a second locus is at 4q. Although the ADPKD1 gene is responsible for the majority of the disease in whites, there was no information regarding the gene type in blacks. We studied a black family which presented with both ADPKD and sickle-cell trait (SA) to determine which ADPKD gene was present in this family, and to examine linkage between the ADPKD in this family and markers for the beta-hemoglobin gene on chromosome 11. The ADPKD in this family was linked to markers on chromosome 16, and no linkage was found with the beta-hemoglobin gene. Family members with SA and ADPKD had an early onset of end-stage renal disease. The hemoglobin haplotype was identified as the Central African Republic-type, which has been reported to be associated with a higher incidence of renal failure in sickle-cell anemia.

Adult↗
PubMed1996

Recommendations for the selection and use of protocols for assignment of values to reference materials.

It is essential that testing of patient samples give values that are traceable to those in a recognized, authorizative reference material. In addition, samples used for laboratory proficiency testing must have values assigned from such a reference material if results are to be comparable among materials and laboratories. As a result, the assignment of values to secondary and tertiary reference materials, calibrants, controls, and proficiency samples should be performed as precisely as possible, within reasonable limits. The intent of this document is to give guidelines for assignment of values at three levels of transfer. 1) from primary to secondary reference, materials, such as international or national references; 2) from secondary to tertiary reference materials, such as manufacturers' in-house calibrants and controls; and 3) from tertiary reference materials, such as manufacturers' in-house calibrants and controls; and 3) from tertiary reference materials to working calibrants and controls. It is hoped that these guidelines will facilitate the selection and utilization of an appropriate value transfer protocol for each level of value assignment. Because of the wide variety and nature of analytes, however, the guidelines are intentionally broad and may require revision for specific analytes.

Calibration↗
PubMed1996

Consensus of a group of professional societies and diagnostic companies on guidelines for interim reference ranges for 14 proteins in serum based on the standardization against the IFCC/BCR/CAP Reference Material (CRM 470). International Federation of Clinical Chemistry. Community Bureau of Reference of the Commission of the European Communities. College of American Pathologists.

The release in 1993 of a new reference material for serum proteins, CRM 470/RPPHS 5 has given rise to a great improvement in the between-laboratory variability of serum protein measurements worldwide. Conversion to the new reference material results in significant changes in reference values for some proteins. The establishment of new reference ranges will take a considerable time, and in the interim several professional societies and diagnostic companies have agreed to use consensus reference ranges based on studies already undertaken.

Blood Proteins↗
PubMed1996

Ethnic differences in women with HIV infection in Britain and Ireland. The study group for the mrc collaborative study of HIV infection in women.

OBJECTIVE: To examine ethnic differences in the socio-epidemiological and clinical characteristics of a cohort of women with HIV infection in Britain and Ireland. DESIGN AND METHODS: Analysis of baseline data (ethnic group, sexual history, likely route of HIV infection, reasons for HIV testing and first AIDS-defining disease) from 400 women with HIV infection recruited into a cohort study from 15 genitourinary medicine/HIV clinics in Britain and Ireland. RESULTS: Sixty-five per cent of women were white and 29% black African. Their median number of lifetime sexual partners was seven and three, respectively (P < 0.001). Ninety-three per cent of black African and 43% of white women were probably infected through sexual intercourse. Injecting drug use was the most likely route of infection in 55% of white women, but none of the black African women. Perceived risk (33%) or investigation of symptoms (26%) were the most common reasons for HIV testing. Seven per cent of white women and 16% of black African women (P < 0.001) had AIDS when HIV infection was diagnosed. The distribution of first AIDS-defining diagnoses differed (P = 0.001) by ethnic group. For white women, the most common disease was Pneumocystis carinii pneumonia; for black African women it was pulmonary tuberculosis. CONCLUSION: There are important differences between black African and white women in sexual history and route of transmission, disease stage at diagnosis and pattern of AIDS-defining diseases.

AIDS Serodiagnosis↗
PubMed1996

Experimentally induced Bartonella henselae infections followed by challenge exposure and antimicrobial therapy in cats.

OBJECTIVES: To elucidate kinetics of Bartonella henselae bacteremia and IgG response, evaluate antibiotic therapy, and investigate challenge exposure in cats. ANIMALS: Specific-pathogen-free cats. PROCEDURE: Cats were inoculated with B henselae or B quintana and monitored. Convalescent cats were challenge exposed with B henselae. Amoxicillin, enrofloxacin, erythromycin, and tetracycline HCl were evaluated for effect on B henselae bacteremia. RESULTS: Cats developed B henselae bacteremia within 1 week; bacteremia persisted for longer than 2 months before subsiding spontaneously. IgG antibody titer developed shortly after onset of bacteremia; antibody co-existed with bacteremia for several weeks and remained detectable after bacteremia subsided. Cats inoculated with B quintana remained abacteremic. On challenge exposure to B henselae, cats previously infected with B henselae remained abacteremic; cats previously inoculated with B quintana supported B henselae infection. Tetracycline HCl and erythromycin depressed B henselae bacteremia; however, duration of bacteremia remained similar to that in untreated cats. Obvious signs of illness were not observed. CONCLUSIONS: Long-duration, high-titer B henselae infections were highly reproducible in cats. Convalescent cats were immune to reinfection. B quintana-inoculated cats did not have evidence of infection and were susceptible to B henselae challenge exposure. Antibiotic therapy was incompletely efficacious in terminating cat bacteremia. CLINICAL RELEVANCE: A cat with an inapparent B henselae infection must provisionally be regarded as a possible reservoir for infection for a minimum of 2 to 3 months. Convalescent cats are resistant to reinfection. Usual antibiotic therapy was not completely efficacious. Measurement of IgG antibody can be used to detect past or current infection.

Amoxicillin↗
PubMed1996

Genetic diversity in Sarcocystis gigantea assessed by RFLP analysis of the ITS1 region.

The genetic diversity among Sarcocystis gigantea isolates derived from individual cysts within a given infected animal at two abattoirs in Australia and one abattoir in Germany was studied using Restriction Fragment Length Polymorphism (RFLP) analysis of the intergenic transcribed spacer region 1 (ITS 1) of the ribosomal RNA gene operon. S. gigantea isolates were obtained from infected sheep from Blayney (New South Wales), Katanning (Western Australia), and Detmold (North-Rhine Westfalia, Germany) in order to assess the level of diversity among isolates from different geographic locations. Polymerase chain reaction amplification and RFLP analysis of the ITSI region with the restriction enzymes HaeIII, NlaIII, and Sau3AI found no genetic variation among the isolates within one animal or among animals in the same or different locations. To our knowledge, such a field study has not yet been performed on a species in the genus Sarcocystis.

Animals↗
PubMed1995

Case-control study of antenatal and intrapartum risk factors for cerebral palsy in very preterm singleton babies.

The increase in survival of very preterm babies during the 1980s was accompanied by a sharp increase in the rate of cerebral palsy in this group. The relation between antenatal and intrapartum factors and cerebral palsy in such babies has not been well defined. To identify adverse and protective antenatal and intrapartum factors we undertook a case-control study of 59 very preterm babies who developed cerebral palsy, identified from a population-based register, and 234 randomly selected controls. The frequency of cerebral palsy decreased with increasing gestational age and birthweight. Antenatal complications occurred in 215 (73%) of the women with preterm deliveries. Factors associated with an increased risk of cerebral palsy after adjustment for gestational age were chorioamnionitis (odds ratio 4.2 [95% CI 1.4-12.0]) prolonged rupture of membranes (2.3 [1.2-4.2]), and maternal infection (2.3 [1.2-4..5]). Pre-eclampsia was associated with a reduced risk of cerebral palsy (0.4 [0.2-0.9]), as was delivery without labour (0.3 [0.2-0.7]). There was no increased risk of cerebral palsy with intrauterine growth retardation (1.0 [0.9-1.1]). The effect of rigorous management of adverse antenatal factors on the frequency of cerebral palsy in very preterm babies should be tested in randomised controlled trials.

Apgar Score↗
PubMed1995

Provision of sex education and early sexual experience: the relation examined.

OBJECTIVES: To explore the relation between receipt of sex education and experience of first intercourse. SUBJECTS AND DESIGN: The national survey of sexual attitudes and lifestyles is based on a sample of 18,876 respondents aged 16-59, randomly selected from the Post Office's small-user postcode address file. Data were collected between May 1990 and November 1991 by personal interviews combining a self administered questionnaire with a face to face interview. MAIN OUTCOME MEASURES: Age at first intercourse, use of contraception at first intercourse, actual and preferred source of sex education (including school based lessons). RESULTS: Median age at first intercourse fell by four years for women and three years for men over the past four decades, to 17 for both men and women aged 16-19 at the time of interview. Of those respondents for whom school was the main source of information about sexual matters, men were less likely, and women no more likely, to have had intercourse before the age of 16 than were those citing other main sources, such as friends and the media. Both men and women were more likely to have used some method of contraception. In multivariate analysis, these effects remained after controlling for the effect of current age, educational attainment, and religious affiliation. CONCLUSIONS: These data provide no evidence to support the concern that provision of school sex education might hasten the onset of sexual experience. These findings have important implications for the provision of sexual health education and highlight the need to carry out prospective and randomised studies of the impact of sex education.

Adolescent↗
PubMed1995

Genetic comparison of Neospora caninum with Toxoplasma and Sarcocystis by random amplified polymorphic DNA-polymerase chain reaction.

To determine the relationship of Neospora caninum to protozoa classified in the family Sarcocystidae of the phylum Apicomplexa, the genomes of N. caninum, three Toxoplasma gondii strains (RHa, CEP, TPR) and three Sarcocystis species (S. tenella, S. muris, S. gigantea) that were thought to be closely related coccidia were compared by the random amplified polymorphic DNA (RAPD) polymerase chain reaction (PCR) technique. The genomic DNAs were amplified by the use of seven 10-mer arbitrary sequence primers to generate polymorphic DNA. Significant DNA polymorphisms were observed among Neospora, Toxoplasma and Sarcocystis. It appears that one primer tested may have value in a diagnostic RAPD-PCR to differentiate T. gondii from other closely related protozoa. The high level of genetic divergence of N. caninum from T. gondii strains and several Sarcocystis species observed in this study is consistent with the hypothesis that N. caninum is indeed an independent species of protozoan parasite. As compared with the Sarcocystis species tested, a closer genetic relationship of N. caninum to T. gondii was not observed. By contrast, a closer genetic relationship of S. muris to T. gondii was revealed in this study.

Animals↗
PubMed1995

Genetic differentiation of pathogenic and nonpathogenic strains of Entamoeba histolytica by random amplified polymorphic DNA polymerase chain reaction.

The random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) method was used to compare pathogenic and nonpathogenic strains of Entamoeba histolytica. DNA polymorphisms were detected among the different strains and dendrograms were constructed by PHYLIP and PAUP analyses to study the relationship of the strains. Both analyses resulted in identical results, which indicated that pathogenic strains of E. histolytica are closely related and clearly separated from the nonpathogenic strains. The results of this study agree with classification of the strains based on isoenzyme analyses. This suggests that RAPD-PCR is a valuable method in differentiating between strains of this parasite, and the results are consistent with the concept that pathogenic and nonpathogenic Entamoeba represent two different species.

Animals↗
PubMed1995

Genetic characterization of Toxoplasma gondii strains by random amplified polymorphic DNA polymerase chain reaction.

The technique of Random Amplified Polymorphic DNA (RAPD) PCR has been used to detect DNA polymorphisms among Toxoplasma gondii strains. Seven arbitrary oligonucleotides (10-mer) were used as primers to amplify total genomic DNAs and significant genetic heterogeneity was detected among 11 T. gondii strains with different virulence for mice. The polymorphisms observed allowed relationship dendrograms of T. gondii strains to be constructed by PHYLIP and PAUP analyses. The genetic relationships of the T. gondii strains generated by 2 analyses using completely different assumptions were similar. Both analyses revealed 2 groups of T. gondii strains, one formed by the 6 virulent strains and the other formed by the 5 avirulent strains. This suggests that the genus Toxoplasma may actually contain 2 groups, correlated with their virulence, which have probably evolved independently following their initial separation. Significant polymorphisms were also detected between 2 different laboratory stocks of the T. gondii RH strain.

Animals↗