Long-term course of Mycobacterium tuberculosis infection in Swedish birth cohorts during the twentieth century.

SETTING: Sweden under transition from high to low tuberculosis (TB) incidence from 1920 to 2009. OBJECTIVE: To correlate estimates of TB infection in birth cohorts with the longitudinal incidence of active TB to assess the long-term risk and time pattern of reactivated TB. DESIGN: Time trend analysis on TB incidence using age-cohort modelling. RESULTS: The overall TB incidence decreased from 700 per 100,000 population in 1920 to 1.4 in 2009 in the Sweden-born population. The estimated disease rate (number of cases divided by the estimated number of infected in 1967), for each birth cohort between 1920 and 1940, was stable on a level between 9.8% and 10.7%. The reactivation rate of latent TB infection (LTBI) was 2% after 1967, when indigenous transmission had disappeared. CONCLUSION: Although approximately 10% of persons with LTBI developed active TB, the majority of cases occurred shortly after infection, and the rates of reactivation declined over time. This indicates extensive spontaneous clearance of LTBI.

Evaluating the usefulness of spa typing, in comparison with pulsed-field gel electrophoresis, for epidemiological typing of methicillin-resistant Staphylococcus aureus in a low-prevalence region in Sweden 2000-2004.

The usefulness of spa typing was evaluated in relation to pulsed-field gel electrophoresis (PFGE), as a tool for epidemiological typing of methicillin-resistant Staphylococcus aureus (MRSA) in a low-prevalence region in southern Sweden. Bacterial isolates from 216 MRSA cases, newly identified in 2000-2004, were studied. The isolates were obtained from infected patients (31%), and from colonized individuals found by screening (69%). In total, 49 spa types and 73 PFGE patterns were identified. The discriminatory power of spa typing was lower (94.9 +/- 1.8%) than that of PFGE (97.3 +/- 1.2%). For two spa types (t002 and t008) the Panton-Valentine leukocidin results added useful discriminatory information. The most common spa types were t044 (n = 31; four PFGE patterns), t002 (n = 24; 10 PFGE patterns), t067 (n = 12; four PFGE patterns), t050 (n = 12; one PFGE pattern), and t324 (n = 11; one PFGE pattern). Epidemiological investigations identified 91 single cases and 39 transmission chains, each involving two to 13 cases. All the transmission chains were held together both by spa and PFGE typing. Among the 91 single-case isolates, 33 spa types and 50 PFGE patterns were unique (matchless) at the time of identification. The low prevalence of MRSA, the low number of outbreaks, and the wide spectrum of strains due to frequent acquisitions abroad (49% of the cases), makes spa typing a useful complement to epidemiological investigations in our setting. However, we still recommend the continued use of PFGE for further discrimination of isolates with identical spa types when epidemiological data can not exclude possible transmission.

Comparison of strand displacement and ligase chain amplification for detection of Chlamydia trachomatis infection in urogenital specimens.

Two amplification tests for the diagnosis of Chlamydia trachomatis infection, namely the ligase chain reaction (LCx) and the strand displacement assay (ProbeTec), were compared using samples from 1183 patients at sexually transmitted disease clinics. The overall prevalence of positive results was 8.0%, with agreement between the two assays of 98.8%. For endocervical, urethral and male urine samples, agreement was 99.3%, 99.4% and 97.7%, respectively. For ten discrepant samples, alternative amplification assays suggested that the LCx and ProbeTec assays gave erroneous results in six and four cases, respectively. Inhibition of amplification was observed with three (0.25%) urine specimens.

Characterization of isoniazid-resistant strains of Mycobacterium tuberculosis on the basis of phenotypic properties and mutations in katG.

Forty isoniazid-resistant Mycobacterium tuberculosis isolates were characterized on the basis of phenotypic properties (i.e., catalase activity, MIC of isoniazid, and growth pattern in the presence of 7 different concentrations of isoniazid) and alterations in the katG gene (codons 315 and 463). Three different growth patterns could be distinguished: concentration-dependent inhibition of growth was observed in 29 strains, similar growth at all concentrations was seen in 7 strains, and enhanced growth at low concentrations of isoniazid was evident in 4 strains. The MIC of isoniazid was < or = microg/ml for 29 of 40 strains. Mutation at codon 315 of the katG was detected in 28 of 40 strains. However, only one of the seven strains for which the MIC of isoniazid was > or = 16 microg/ml had mutation at this codon. Five of these seven strains for which the MIC was > or = 16 microg/ml had no catalase activity. The results indicate that the MIC of isoniazid for a majority of strains is below the level achievable in serum. Therefore, isoniazid may be beneficial for the treatment of some cases of multidrug-resistant tuberculosis. Determination of catalase activity aids in the detection of isolates for which MICs are high and could, in conjunction with molecular methods, provide rapid detection of most isoniazid-resistant strains.

Comparison between comparative tuberculin and gamma-interferon tests for the diagnosis of bovine tuberculosis in Ethiopia.

A study to determine and compare the sensitivities and specificities of the comparative cervical tuberculin (CCT) and gamma-interferon (IFN-gamma) tests for the diagnosis of bovine tuberculosis was conducted on 30 zebu oxen. The results of the tests were compared with the presence of acid-fast bacilli found by bacteriological culturing and histopathological examinations. The sensitivity and specificity of CCT test were found to be 90.9% and 100%, respectively. Those of the commercial IFN-gamma test were determined to be 95.5% and 87.7%, respectively. No significant differences were found between the sensitivities (Yates' corrected chi 2 = 0.32; p = 0.57) or the specificities (Yates' corrected chi 2 = 2.54; p = 0.11) of the two tests. Furthermore, a positive correlation (r = 0.76) was recorded between the increase in skin thickness following injection of bovine purified protein derivative (PPD) and the optical density in the gamma-interferon assay with bovine PPD. On the other hand, the correlation (r = 0.47) between the change in skin thickness following injection of avian PPD and the optical density in the gamma-interferon assay with avian PPD was relatively weak. On the basis of this preliminary investigation, it was concluded that the choice between the two tests depends on their cost and simplicity and on livestock management and time factors rather than on their respective diagnostic value.

Fluorescence In situ hybridization assay using peptide nucleic acid probes for differentiation between tuberculous and nontuberculous mycobacterium species in smears of mycobacterium cultures.

TB PNA FISH is a new fluorescence in situ hybridization (FISH) method using peptide nucleic acid (PNA) probes for differentiation between species of the Mycobacterium tuberculosis complex (MTC) and nontuberculous mycobacteria (NTM) in acid-fast bacillus-positive (AFB+) cultures is described. The test is based on fluorescein-labelled PNA probes that target the rRNA of MTC or NTM species applied to smears of AFB+ cultures for microscopic examination. Parallel testing with the two probes serves as an internal control for each sample such that a valid test result is based on one positive and one negative reaction. TB PNA FISH was evaluated with 30 AFB+ cultures from Denmark and 42 AFB+ cultures from Thailand. The MTC-specific PNA probe showed diagnostic sensitivities of 84 and 97%, respectively, and a diagnostic specificity of 100% in both studies, whereas the NTM-specific PNA probe showed diagnostic sensitivities of 91 and 64%, respectively, and a diagnostic specificity of 100% in both studies. The low sensitivity of the NTM-specific PNA probe in the Thai study was due to a relatively high prevalence of Mycobacterium fortuitum, which is not identified by the probe. In total, 63 (87%) of the cultures were correctly identified as MTC (n = 46) or NTM (n = 17), whereas the remaining 9 were negative with both probes and thus the results were inconclusive. None of the samples were incorrectly identified as MTC or NTM; thus, the predictive value of a valid test result obtained with TB PNA FISH was 100%.

Usefulness of spoligotyping To discriminate IS6110 low-copy-number Mycobacterium tuberculosis complex strains cultured in Denmark.

Mycobacterium tuberculosis complex strains cultured in Denmark have been analyzed by IS6110 restriction fragment length polymorphism (RFLP) on a routine basis from 1992 and onwards. Due to the influx of immigrants with tuberculosis, the number of strains harboring only one to five copies of IS6110 has increased steadily. Since the discriminatory power of IS6110 fingerprinting for such strains is poor, we have performed additional genotyping of all low-copy-number strains by the recently described PCR-based method known as spoligotyping. A total of 311 clinical strains were typed: 14 Mycobacterium bovis BCG, 48 M. bovis, and 249 M. tuberculosis strains. Spoligotyping correctly differentiated M. bovis and M. bovis BCG from M. tuberculosis strains, but it did not differentiate M. bovis from M. bovis BCG. All M. bovis BCG strains exhibited identical spoligotype patterns. The discriminatory power of spoligotyping of low-copy-number M. tuberculosis strains was higher than that of IS6110 fingerprinting. Based on RFLP typing solely, 83% of the low-copy-number M. tuberculosis strains were found to form part of a cluster, and 75% were found to form a cluster on the basis of spoligotyping. When the two techniques were combined, the amount of clustering decreased to 55%. The combination of these two techniques might be valuable in studying the epidemiology of M. tuberculosis strains harboring few copies of the IS6110 element.

[Tuberculosis in Denmark 1972-1996]. / Tuberkuloseudviklingen i Danmark 1972-1996.

The present study is based on notified cases of tuberculosis (TB) in the National tbc. register 1972-1996. A decline in Tb incidence was seen from 1972 and until the mid-1980's. Subsequently the trend has reversed due to an increasing number of TB cases in foreigners. In 1996, 60% of all cases of TB in Denmark were found in foreigners reflecting the rising number of refugees and their families arriving in Denmark from highly endemic areas, mainly Somalia. Among native Danes the TB incidence fell from 14 per 100,000 in 1972 to 4 per 100,000 in the 1980's and stabilized at this very low level. The unchanged incidence in Danes covers a falling incidence in the older and a rising incidence in the younger and middle-aged adult population, mainly in the capital. Approximately half of the cases occur in high-risk groups. The TB-epidemic is close to elimination in the indigenous Danish population, but the disease is maintained at a low level probably due to increased patient and doctor delay and resulting microepidemics primarily in high-risk populations.

Reactions of N-N and N-O compounds with horseradish peroxidase and peroxidases from Mycobacterium tuberculosis.

Several N-N-and N-O-containing compounds were analysed for their ability to act as substrates for horseradish peroxidase and peroxidases in Mycobacterium tuberculosis extracts. Aminoguanidine, diaminoguanidine, isoniazid, hydroxylamine and hydrazine were found to be weak substrates for horseradish peroxidase in reaction I and to inhibit the reaction of horseradish peroxidase with hydrogen peroxide. The same compounds inhibited the reaction of Mycobacterium tuberculosis peroxidase-catalase with hydrogen peroxide, and hydroxylamine was found to be a weak substrate for this enzyme. In growth inhibition experiments, diaminoguanidine inhibited the growth of M. tuberculosis H37Rv at 50 microg/mL, but not the growth of two isoniazid-resistant strains. Isonicotinic acid hydroxamate inhibited the reaction of the peroxidases with hydrogen peroxide, but was not itself a substrate and had no growth-inhibitory effects. On the basis of these results we suggest that the effect of isoniazid on growth of M. tuberculosis results from increased oxidative stress due to inhibition of catalase-peroxidase as well as from generation of toxic radicals with the structure [structure in text].

Disk with high oxacillin content discriminates between methicillin-resistant and borderline methicillin-susceptible Staphylococcus aureus strains in disk diffusion assays using a low salt concentration.

A separation between mecA+ strains of Staphylococcus aureus and strains lacking mecA was achieved by the disk diffusion assay and the agar dilution method, utilizing disks containing 5 microg of oxacillin and inocula of approximately 5 x 10(5) CFU/spot, respectively, provided that agar with 0 to 0.5% NaCl and incubation at 30 degrees C were employed. The 5-microg oxacillin disks clearly discriminated between borderline methicillin-susceptible and mecA+ strains. The oxacillin MICs were more affected by the inoculum density and salt concentration than were the methicillin MICs, and oxacillin MICs of 4 to 16 microg/ml were obtained for strains lacking mecA. Significantly higher levels of beta-lactamase production and reduced oxacillin susceptibilities were recorded for strains lacking mecA, in particular strains of phage group V, when agar with >/=2% NaCl was used than when agar with 0 to 0.5% NaCl was employed. The results indicate that the borderline methicillin-susceptible phenotype is a salt-dependent in vitro phenomenon of questionable clinical relevance.

[30 years of successful mycobacteriology research, The AHRI in Addis Abeba--a unique research environment in a developing country]. / 30 år av framgångsrik mykobakterieforskning. AHRI i Addis Abeba--unik forskningsmiljö i u-land.

The Armauer Hansen Research Institute (AHRI) in Addis Abeba, Ethiopia, was established by the Swedish and Norwegian Save the Children organisations in collaboration with the University of Bergen, with the principal objective of pursuing basic research in leprosy. The institute has a commendable record of achievement, and has made significant contributions to our understanding of leprosy and its control, and to the training of scientists from Ethiopia and other African countries. Recently, the Ethiopian, Swedish and Norwegian governments agreed to continue supporting the AHRI as an autonomous research centre. Its main objectives will be to conduct research in mycobacterial diseases, particularly tuberculosis, and to promote the enhancement of human resources in health research through instruction, supervision, and scientific collaboration.

Evaluation of a colorimetric assay based on 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) for rapid detection of rifampicin resistance in Mycobacterium tuberculosis.

OBJECTIVES: To standardise the colorimetric assay based on 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) for the rapid detection of rifampicin-resistant Mycobacterium tuberculosis in clinical practice and to evaluate the assay on a collection of 92 clinical isolates. DESIGN: The Bactec method was used as the reference method. Rifampicin was used for the susceptibility testing in the Bactec method at a concentration of 2 microg/ml. The MTT assay was performed in tubes containing 3 ml Dubos broth; the assay is based on the principle that live cells convert the yellow tetrazolium salt into a blue formazan. A final concentration of 2 microg/ml rifampicin was used in the assay. Optical density (OD) values at 570 nm were recorded on the third and sixth day. A strain was defined as susceptible when the relative optical density unit (RODU) (i.e., OD of rifampicin containing tube/OD of undiluted control) was < or = 0.2, and when the OD value of the rifampicin-containing tube on the sixth day was lower than the OD value on the third day. A strain was defined as resistant when the RODU was more than 0.5, and when there was an increase in OD value in the rifampicin-containing tube on the sixth day. The tubes were also read visually. RESULTS AND CONCLUSION: The result obtained by the MTT assay perfectly matched the result obtained by the Bactec method. The MTT assay was also interpretable by the naked eye. This simple, inexpensive assay could be used as a rapid screening method for identification of rifampicin-resistant strains in low-income countries.

Drug resistance in Mycobacterium tuberculosis strains isolated from re-treatment cases of pulmonary tuberculosis in Ethiopia: susceptibility to first-line and alternative drugs.

SETTING: Addis Ababa Tuberculosis Demonstration and Training Center, Ethiopia. OBJECTIVES: To determine the pattern of drug resistance among re-treatment cases of pulmonary tuberculosis (TB), to determine the risk factors associated with multi-drug resistant (MDR) TB, and to propose re-treatment regimens based on the patterns of susceptibility to first-line and alternative drugs. DESIGN: One hundred and seven Mycobacterium tuberculosis strains isolated from an equal number of re-treatment cases of pulmonary TB were included in the study. Drug susceptibility was determined by the Bactec method. RESULTS: About 50% of the strains were resistant to one or more of the first-line drugs and 12% of the strains were multi-drug resistant, i.e., resistant to both isoniazid and rifampicin. Previous treatment with rifampicin was the most important predictor of MDR-TB. All MDR strains were susceptible to amikacin, ciprofloxacin, ethambutol, ethionamide and clofazimine. CONCLUSION: The WHO re-treatment regimen would theoretically be effective for the treatment of all non-MDR-TB patients in this study. A proposed 12-month re-treatment regimen for MDR-TB patients would include a fluoroquinolone in combination with streptomycin, pyrazinamide, isoniazid, ethambutol and clofazimine. There is an urgent need for more research to define safe and inexpensive treatment regimens for MDR-TB patients in low-income countries.

Use of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide for rapid detection of rifampin-resistant Mycobacterium tuberculosis.

We describe a test which uses the ability of viable cells to reduce 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) to detect resistance to a bactericidal drug, rifampin, in in vitro-cultured Mycobacterium tuberculosis. The assay shows a linear relationship between the number of viable bacteria and the ability to reduce MTT. Dead mycobacteria were unable to reduce MTT. Rifampin-sensitive M. bovis (BCG) and M. tuberculosis exposed to rifampin showed a rifampin concentration-dependent inhibition of the ability to reduce MTT, while the resistant strains were unaffected. The inhibition of MTT reduction after treatment with rifampin paralleled the reduction in the number of CFU. By using mixing experiments in which the population percentages of rifampin-sensitive and -resistant strains were varied, the assay could detect the presence of rifampin resistance in the mixture when at least 1% of the bacterial population was composed of drug-resistant strains. The assay is cheap, can be visually read, and requires less than 3 days to obtain susceptibility results. The total time required to obtain results, from the time sputum is received in the laboratory, is, in most cases, less than 4 to 5 weeks, which is the time required for primary culture of the bacteria. The MTT assay could, in combination with a test to detect resistance to isoniazid, be a cheap and rapid screening method for multidrug-resistant M. tuberculosis that is affordable even by low-income countries where tuberculosis is a major public health problem.

Susceptibility of multidrug-resistant strains of Mycobacterium tuberculosis to amoxycillin in combination with clavulanic acid and ethambutol.

Thirty clinical isolates of Mycobacterium tuberculosis, 20 of which were multidrug-resistant (MDR), were tested for susceptibility to different combinations of amoxycillin, clavulanic acid and subinhibitory concentrations of ethambutol. beta-Lactamase production was assessed semiquantitatively with the nitrocefin method and susceptibility testing was performed with the BACTEC method. All isolates were beta-lactamase positive and were resistant to 16 mg/L amoxycillin. The MIC of amoxycillin in combination with clavulanic acid was > or =2 mg/L for 27/30 (90%) isolates. Addition of subinhibitory concentrations of ethambutol significantly reduced the MIC of amoxycillin for all tested isolates. Twenty-nine (97%) isolates had an MIC of amoxycillin of < or =0.5 mg/L when subinhibitory concentrations of ethambutol were added; this is well below the concentrations achievable in serum and tissue.

Detection of Plasmodium falciparum sporozoites in naturally infected anopheline species using a fluorescein-labelled DNA probe.

A dot blot hybridization method was developed to detect Plasmodium falciparum sporozoites in naturally infected mosquitoes. A fluorescein-labelled oligomer was used as a probe. Initial non-specific hybridization was found to correlate with the presence of blood in the mosquitoes. This was eliminated by allowing digestion of the engorged blood by keeping the mosquitoes in cages for 48 h before processing. The limit of detection of the hybridization assay was estimated to be about 500 sporozoites. The assay was evaluated on 198 indoor resting blood fed female Anopheles gambiae s.l mosquitoes collected from three malaria hypo- and meso-endemic areas in Ethiopia. An application of the polymerase chain reaction (PCR) amplifying a fragment of the K1-14 gene of P. falciparum was used as a reference method. P. falciparum sporozoites were detected in four specimens (2%) by hybridization assay and by PCR alike. The results of this study indicate that the hybridization method can be potentially valuable in large scale epidemiological studies for detection of P. falciparum sporozoites in naturally infected anopheline species.

Antimicrobial susceptibility testing in Sweden. III. Methodology for susceptibility testing.

A subcommittee of the Swedish Reference Group for Antibiotics, SRGA-M, has worked with standardization of methodology for susceptibility testing. In vitro data obtained with the disk diffusion procedure were collected from 5 clinical laboratories, compiled and presented as histograms of inhibition zones, and compared with data [minimum inhibitory concentrations (MICs) and inhibition zones] obtained from the reference laboratory at the Swedish Institute for Infectious Disease Control on a collection of clinically relevant bacterial species. Results from the reference collection of strains were presented as MIC histograms, and their corresponding inhibition zones were inserted in the compiled zone histograms as identifiable bars. These distributions formed the basis for decisions of breakpoints. Special tests were recommended for the detection of certain resistance mechanisms. A beta-lactamase test should be used for Haemophilus influenzae, Moraxella catarrhalis, Neisseria gonorrhoeae and enterococci. Screening for beta-lactam resistance caused by altered penicillin binding proteins should be done by using oxacillin 1 microgram for Streptococcus pneumoniae and Staphylococcus aureus (MRSA), and by phenoxymethylpenicillin 10 micrograms for H, influenzae. The standardized disk diffusion procedure was helpful in detecting enterobacteria carrying beta-lactamases with extended spectra. Registration of inhibition zones will provide a powerful tool for the epidemiological surveillance of antibiotic resistance.

Improved sensitivity of direct microscopy for acid-fast bacilli: sedimentation as an alternative to centrifugation for concentration of tubercle bacilli.

There is a great need for improved methods for the diagnosis of tuberculosis by techniques that are appropriate for control programs in low-income countries. Liquefaction of sputum with sodium hypochlorite followed by concentration of bacilli through overnight sedimentation significantly increases the sensitivity of direct microscopy, and this method could be an alternative for diagnostic centers not equipped with a centrifuge.

Acanthamoeba keratitis in the south of Sweden.

Eight patients with Acanthamoeba keratitis were diagnosed and treated at our clinic between February 1991 and February 1993. Five of these were contact lens wearers, two had suffered recent corneal trauma and one had recently undergone penetrating keratoplasty. The diagnoses were based on both culture and histological examination of biopsy material in three cases, on culture alone in two cases and on histological examination alone in three cases. In all but one primary treatment was Propamidine isethionate and Neomycin/Polymyxin B topically and Ketoconazole orally. Because of poor healing three patients additionally received Paromomycin and Miconazole or Clotrimazol topically; two of these were further treated with Polyhexamethylene biguanide topically. The interval from initial symptoms to accurate diagnoses varied from one to eleven months. In one patient the eye could not be saved; in the remaining patients visual acuity after healing ranged from hand movements to 1.0.