Genetic diversity and transmission characteristics of Beijing family strains of Mycobacterium tuberculosis in Peru

Beijing family strains of Mycobacterium tuberculosis have attracted worldwide attention because of their wide geographical distribution and global emergence. Peru, which has a historical relationship with East Asia, is considered to be a hotspot for Beijing family strains in South America. We aimed to unveil the genetic diversity and transmission characteristics of the Beijing strains in Peru. A total of 200 Beijing family strains were identified from 2140 M. tuberculosis isolates obtained in Lima, Peru, between December 2008 and January 2010. Of them, 198 strains were classified into sublineages, on the basis of 10 sets of single nucleotide polymorphisms (SNPs). They were also subjected to variable number tandem-repeat (VNTR) typing using an international standard set of 15 loci (15-MIRU-VNTR) plus 9 additional loci optimized for Beijing strains. An additional 70 Beijing family strains, isolated between 1999 and 2006 in Lima, were also analyzed in order to make a longitudinal comparison. The Beijing family was the third largest spoligotyping clade in Peru. Its population structure, by SNP typing, was characterized by a high frequency of Sequence Type 10 (ST10), which belongs to a modern subfamily of Beijing strains (178/198, 89.9%). Twelve strains belonged to the ancient subfamily (ST3 [n=3], ST25 [n=1], ST19 [n=8]). Overall, the polymorphic information content for each of the 24 loci values was low. The 24 loci VNTR showed a high clustering rate (80.3%) and a high recent transmission index (RTI(n-1)=0.707). These strongly suggest the active and on-going transmission of Beijing family strains in the survey area. Notably, 1 VNTR genotype was found to account for 43.9% of the strains. Comparisons with data from East Asia suggested the genotype emerged as a uniquely endemic clone in Peru. A longitudinal comparison revealed the genotype was present in Lima by 1999.

Second-line anti-tuberculosis drug concentrations for susceptibility testing in the MODS assay

Multidrug-resistant tuberculosis (TB) threatens TB control worldwide. The microscopic observation drug susceptibility (MODS) assay is a low-cost, high-performance TB diagnostic tool for rapid liquid culture and direct isoniazid and rifampicin drug susceptibility testing (DST). The objective of this study was to explore the potential for extending the MODS assay to rapid second-line DST and to identify critical concentrations of candidate drugs for prospective testing. Sputum samples from 94 TB culture-positive patients receiving second-line TB agents were cultured following standardised MODS protocols, with a range of titrations of antimicrobial drugs added. Critical concentrations were determined using a modified Kaplan-Meier survival curve analysis. Candidate critical concentrations were determined for capreomycin (10 μg·mL(-1)), ciprofloxacin (1.25 μg·mL(-1)), cycloserine (40 μg·mL(-1)), ethambutol (10 μg·mL(-1)), ethionamide (5 μg·mL(-1)), kanamycin (5 μg·mL(-1)), para-aminosalicylic acid (10 μg·mL(-1)) and streptomycin (10 μg·mL(-1)). No cut-off point was identified for the other second-line drugs or for pyrazinamide. At particular concentrations of some second-line TB drugs this novel Kaplan-Meier analysis clearly differentiated populations that were susceptible or resistant. These candidate critical concentrations should now be tested in a range of epidemiological settings to define the performance of direct, second-line TB DST with MODS, offering potential low-cost second-line TB DST capacity.

Tuberculosis in household contacts of multidrug-resistant tuberculosis patients

SETTING

The burden of tuberculosis (TB) disease among household contacts of multidrug-resistant TB (MDR-TB) patients is poorly understood and might represent a target for transmission-interrupting interventions.

DESIGN

This retrospective cohort study, conducted in Lima, Peru, from June to September 2008, estimated the incidence of TB disease among household contacts of MDR-TB patients in 358 households.

RESULTS

Of 2112 household contacts in 80 households (22% of households), 108 (5%) developed TB disease during the study, giving an incidence rate of 2360 per 100 000 contact follow-up years for each of the first 3 years after exposure. Drug susceptibility tests (DST) were available for 50 diseased contacts, of whom 36 (80%) had MDR-TB. Forty-two pairs of index-contact DSTs were available, among which the contact had an identical or less resistant phenotype than the index case in 27 pairs. Multivariate Cox regression demonstrated that male contacts (hazard ratio [HR] 2.8, P < 0.05), with previous TB disease (HR 20.7, P < 0.001) and with associated (non-human immunodeficiency virus) comorbidities (HR 11.2, P < 0.001) were more likely to develop TB.

CONCLUSION

The high percentage of diseased household contacts highlights an opportunity for household-level interventions to prevent transmission, whether or not these cases were all attributable to the index case.

Alternative methods of diagnosing drug resistance--what can they do for me?

During the last decade considerable attention has been focussed upon the development of new technologies and methodologies for detection of drug resistance in Mycobacterium tuberculosis. There is a growing acknowledgement that the redundancy in testing a full panel of first-line drugs is an unaffordable indulgence; since only resistance at baseline to either (or both) of the two most potent agents, isoniazid (H) and rifampicin (R), would usually prompt therapeutic modification there is a shift towards initial RH (or R alone for selected genotypic technologies) drug susceptibility testing (DST) followed, if necessary by further extended first and second line agent (currently phenotypic) DST. Most of the new drug susceptibility tests endorsed by the World Health Organization since 2007 deliver rapid RH (or R alone for selected genotypic technologies) DST. Targeting of patient groups with risk factors for drug resistance increases the proportion of tests that identify drug resistance, but in many settings at least as many patients with drug resistant disease will have no identifiable risk factors--equity of care demands that universal RH DST at baseline should be the goal. We review the bewildering array of choices facing TB program directors and attempt to provide objective information to help in deciding what tools may be best suited to different environments.

Reliability of the MODS assay decentralisation process in three health regions in Peru

OBJECTIVE

To deliver rapid isoniazid (INH) and rifampicin (RMP) drug susceptibility testing (DST) close to the patient, we designed a decentralisation process for the microscopic observation drug susceptibility (MODS) assay in Peru and evaluated its reliability.

METHODS

After 2 weeks of training, laboratory staff processed ≥ 120 consecutive sputum samples each in three regional laboratories. Samples were processed in parallel with MODS testing at an expert laboratory. Blinded paired results were independently analysed by the Instituto Nacional de Salud (INS) according to pre-determined criteria: concordance for culture, DST against INH and RMP and diagnosis of multidrug-resistant tuberculosis (MDR-TB) ≥ 95%, McNemar's P > 0.05, kappa index (κ) ≥ 0.75 and contamination 1-4%. Sensitivity and specificity for MDR-TB were calculated.

RESULTS

The accreditation process for Callao (126 samples, 79.4% smear-positive), Lima Sur (n = 130, 84%) and Arequipa (n = 126, 80%) took respectively 94, 97 and 173 days. Pre-determined criteria in all regional laboratories were above expected values. The sensitivity and specificity for detecting MDR-TB in regional laboratories were >95%, except for sensitivity in Lima Sur, which was 91.7%. Contamination was 1.0-2.3%. Mean delay to positive MODS results was 9.9-12.9 days.

CONCLUSION

Technology transfer of MODS was reliable, effective and fast, enabling the INS to accredit regional laboratories swiftly.

Missed opportunities for tuberculosis diagnosis

BACKGROUND

In high tuberculosis (TB) burden, resource-poor countries, sputum smear microscopy remains the mainstay of diagnosis. The low sensitivity of this test means that patients with smear-negative but culture-positive TB pass undetected through the health care system. Such clinical episodes are missed opportunities for diagnosis and interruption of transmission, which might be averted through the application of more sensitive diagnostic tests.

OBJECTIVES

To estimate the proportion of incident TB cases that might have been detected earlier than the actual date of diagnosis if a test more sensitive than smear microscopy had been used at an earlier presentation episode.

METHOD

Retrospective cohort study in urban Peru, investigating health care facility interactions for symptoms suggestive of TB prior to TB diagnosis through patient interviews and a review of clinical records.

RESULTS

Of 212 participants enrolled, 58% had one or more clinical interactions prior to their diagnostic episode. Of those with a prior episode, the median number of episodes was three. The median delay to diagnosis from first presentation was 26 days.

CONCLUSION

There are clear missed opportunities for earlier TB diagnosis, delaying treatment initiation and continued spread of Mycobacterium tuberculosis to the community. The implementation of sensitive diagnostic tests appropriate to resource-poor settings should be given high priority.

Development of an automated MODS plate reader to detect early growth of Mycobacterium tuberculosis

In this work, an automated microscopic observation drug susceptibility (MODS) plate reader has been developed. The reader automatically handles MODS plates and after autofocussing digital images are acquired of the characteristic microscopic cording structures of Mycobacterium tuberculosis, which are the identification method utilized in the MODS technique to detect tuberculosis and multidrug resistant tuberculosis. In conventional MODS, trained technicians manually move the MODS plate on the stage of an inverted microscope while trying to locate and focus upon the characteristic microscopic cording colonies. In centres with high tuberculosis diagnostic demand, sufficient time may not be available to adequately examine all cultures. An automated reader would reduce labour time and the handling of M. tuberculosis cultures by laboratory personnel. Two hundred MODS culture images (100 from tuberculosis positive and 100 from tuberculosis negative sputum samples confirmed by a standard MODS reading using a commercial microscope) were acquired randomly using the automated MODS plate reader. A specialist analysed these digital images with the help of a personal computer and designated them as M. tuberculosis present or absent. The specialist considered four images insufficiently clear to permit a definitive reading. The readings from the 196 valid images resulted in a 100% agreement with the conventional nonautomated standard reading. The automated MODS plate reader combined with open-source MODS pattern recognition software provides a novel platform for high throughput automated tuberculosis diagnosis.

Novel developments in the epidemic of human immunodeficiency virus and tuberculosis coinfection

Tuberculosis (TB) disease remains one of the highest causes of mortality in HIV-infected individuals, and HIV-TB coinfection continues to grow at alarming rates, especially in sub-Saharan Africa. Surprisingly, a number of important areas regarding coinfection remain unclear. For example, increased risk of TB disease begins early in the course of HIV infection; however, the mechanism by which HIV increases this risk is not well understood. In addition, there is lack of consensus on the optimal way to diagnose latent TB infection and to manage active disease in those who are HIV infected. Furthermore, effective point-of-care testing for TB disease remains elusive. This review discusses key areas in the epidemiology, pathogenesis, diagnosis, and management of active and latent TB in those infected with HIV, focusing attention on issues related to high- and low-burden areas. Particular emphasis is placed on controversial areas where there are gaps in knowledge and on future directions of study.

The MIT D-lab electricity-free PortaTherm™ incubator for remote testing with the QuantiFERON®-TB Gold In-Tube assay

BACKGROUND

Use of the QuantiFERON®-TB Gold In-Tube assay (QFT-GIT) in remote areas is limited by the need to incubate blood samples within 12 h of collection. PortaTherm™ is a portable, electricity-free, phase-change incubator previously used for field collection of microbiological samples.

OBJECTIVE

To determine whether the PortaTherm can be used for the reliable incubation of QFT-GIT samples, thus enabling QFT-GIT use in settings distant from laboratory facilities.

METHODS

In a prospective comparative study in Peru, blood samples were collected from 50 participants and processed in three parallel QFT-GIT tests per participant; two were incubated in a conventional incubator; the third was incubated in the PortaTherm.

RESULTS

All 150 QFT-GIT tests gave definitive results, and for 46 of the 50 participants all three tests were concordant, eight of which were positive. Four participants had one discordant result: two due to discordance of a conventional incubator QFT-GIT result, and two due to discordant PortaTherm QFT-GIT results.

CONCLUSION

The QFT-GIT inter-incubator variability between the PortaTherm and conventional incubator was no greater than the intra-incubator variability for the conventional incubator, indicating that the PortaTherm is a suitable tool for incubating QFT-GIT whole blood samples in remote settings where access to a laboratory or electricity is limited.

MODS accreditation process for regional reference laboratories in Peru: validation by GenoType® MTBDRplus

SETTING

Although considerable effort has been put into the development and evaluation of new diagnostics for tuberculosis (TB) and multidrug-resistant TB (MDR-TB), little attention has thus far been paid to the technical aspects of initiating quality-assured routine service use. For implementation of the microscopic-observation drug susceptibility (MODS) methodology in the Peruvian reference laboratory network, a laboratory accreditation process was devised; MODS results from an expert reference laboratory (Universidad Peruana Cayetano Heredia [UPCH]) were used as the standard against which implementing laboratory MODS results were judged to ensure that, prior to use for patient care, implementing laboratories achieved the same high performance with MODS as previously demonstrated in the research laboratory.

OBJECTIVE

To evaluate the validity of MODS-based accreditation and the concordance of MODS drug susceptibility testing (DST) with molecular testing.

DESIGN

Head-to-head comparison of MODS DST results from implementing Peruvian regional reference laboratories and the accrediting expert MODS laboratory (UPCH) with GenoType® MTBDRplus DST.

RESULTS

The concordance of phenotypic MODS rifampicin (RMP) DST with GenoType MTBDRplus was respectively 97.4%, 97.9% and 97.1% for the two implementing regional laboratories and UPCH, and respectively 94.7%, 95.7% and 94.6% for isoniazid (INH) DST.

CONCLUSION

High and consistent levels of MODS/MTBDRplus concordance for INH and RMP DST confirm the validity of the use of rapid methods as reference standards for accreditation.

Prolonged infectiousness of tuberculosis patients in a directly observed therapy short-course program with standardized therapy

BACKGROUND

Effective tuberculosis control is compromised by a lack of clarity about the timeframe of viable Mycobacterium tuberculosis shedding after treatment initiation under programmatic conditions. This study quantifies time to conversion from smear and culture positivity to negativity in unselected tuberculosis patients receiving standardized therapy in a directly observed therapy short-course (DOTS) program.

METHODS

Longitudinal cohort study following up 93 adults initiating tuberculosis therapy in Lima, Peru. Baseline culture and drug susceptibility tests (DSTs) were performed using the MBBacT, proportion, and microscopic observation drug susceptibility (MODS) methods. Smear microscopy and MODS liquid culture were performed at baseline and weekly for 4 weeks then every other week for 26 weeks.

RESULTS

Median conversion time from culture positivity to culture negativity of 38.5 days was unaffected by baseline smear status. Patients with fully susceptible tuberculosis had a median time to culture conversion of 37 days; 10% remained culture positive at day 60. Delayed culture conversion was associated with multidrug resistance, regardless of DST method used; non-multidrug resistance as defined by the proportion method and MODS (but not MBBacT) was also associated with delay. Persistent day 60 smear positivity yielded positive and negative predictive values of 67% and 92%, respectively, for detecting multidrug resistance.

CONCLUSIONS

Smear and culture conversion in treated tuberculosis patients takes longer than is conventionally believed, even with fully susceptible disease, and must be accounted for in tuberculosis treatment and prevention programs. Persistent day 60 smear positivity is a poor predictor of multidrug resistance. The industrialized-world convention of universal baseline DST for tuberculosis patients should become the standard of care in multidrug resistance-affected resource-limited settings.

Tuberculosis transmission risk and infection control in a hospital emergency department in Lima, Peru

BACKGROUND

Overcrowded emergency departments (EDs) are used by undiagnosed tuberculosis (TB) patients. TB infection control measures are seldom prioritized, making EDs potential foci of unrecognised nosocomial transmission.

OBJECTIVE

To quantify TB infection risk among health care workers in an ED in a high TB-burden setting, Lima, Peru, and to evaluate TB infection control measures.

METHODS

Consenting ED staff were tested for TB infection at baseline and after 1 year using the QuantiFERON-TB Gold In-Tube (QFT-G). In parallel, sputum for TB culture was requested from patients spending >2 h in the ED, irrespective of presenting complaint. Infection control measures were documented and room ventilation measured.

RESULTS

Over 1 year, there were 2246 TB patient-hours of exposure in the ED from 153 different patients. At baseline, 56% of the 70 staff recruited were QFT-G-positive; 27 of 31 baseline-negatives consented to follow-up after 1 year, and eight (30%, all clinical staff) tested positive. Annual incidence of infection was 1730 per 100,000 population. TB infection control measures were sub-optimal, with no patient screening, no isolation rooms, inadequate ventilation and sporadic respirator use.

CONCLUSIONS

ED staff were exposed to an unexpectedly large TB burden in the workplace, resulting in a high rate of TB infection. TB infection control should be prioritized in EDs, especially in high-prevalence settings.

Falls, poisonings, burns, and road traffic injuries in urban Peruvian children and adolescents: a community based study

OBJECTIVES

To identify individual and household characteristics associated with serious falls, poisonings, burns and road traffic injuries (RTIs) for children in Lima, Peru.

METHODS

5061 households consisting of 10,210 children were included in this community based, cross-sectional study in San Juan de Miraflores (SJM), a low income, urban district of Lima, Peru. Households were eligible if there was a consenting adult and at least one resident child aged < or =18 years. A door to door survey was conducted in SJM, collecting childhood injury, demographic, and socioeconomic data. Analysis was done at the individual and household level for injuries severe enough to have required medical consultation.

RESULTS

The greatest burden of injury was from falls and RTIs. For individuals, male gender and age were the most important predictors of injuries. Households in which multiple injuries were reported were more likely to be poor (odds ratio (OR) 1.66, 95% CI 1.24 to 2.22) and overcrowded (OR 1.88, 95% CI 1.20 to 2.94). The occurrence of serious falls, poisonings, burns, and pedestrian RTIs significantly increased the likelihood of a second serious injury in the home (adjusted ORs ranged between 1.88 and 2.99).

CONCLUSION

All children from households in which an unintentional injury has occurred appear to have an increased likelihood of future injury; such high risk households may be readily identifiable in the clinical setting. Interventions in this environment designed to prevent subsequent injuries merit further investigation.

Microscopic observation drug susceptibility assay for tuberculosis screening before isoniazid preventive therapy in HIV-infected persons

BACKGROUND

Active tuberculosis (TB) must be excluded before initiating isoniazid preventive therapy (IPT) in persons infected with human immunodeficiency virus (HIV), but currently used screening strategies have poor sensitivity and specificity and high patient attrition rates. Liquid TB culture is now recommended for the detection of Mycobacterium tuberculosis in individuals suspected of having TB. This study compared the efficacy, effectiveness, and speed of the microscopic observation drug susceptibility (MODS) assay with currently used strategies for TB screening before IPT in HIV-infected persons.

METHODS

A total of 471 HIV-infected IPT candidates at 3 hospitals in Lima, Peru, were enrolled in a prospective comparison of TB screening strategies, including laboratory, clinical, and radiographic assessments.

RESULTS

Of 435 patients who provided 2 sputum samples, M. tuberculosis was detected in 27 (6.2%) by MODS culture, 22 (5.1%) by Lowenstein-Jensen culture, and 7 (1.6%) by smear. Of patients with any positive microbiological test result, a MODS culture was positive in 96% by 14 days and 100% by 21 days. The MODS culture simultaneously detected multidrug-resistant TB in 2 patients. Screening strategies involving combinations of clinical assessment, chest radiograph, and sputum smear were less effective than 2 liquid TB cultures in accurately diagnosing and excluding TB (P<.01). Screening strategies that included nonculture tests had poor sensitivity and specificity.

CONCLUSIONS

MODS culture identified and reliably excluded cases of pulmonary TB more accurately than other screening strategies, while providing results significantly faster than Lowenstein-Jensen culture. Streamlining of the ruling out of TB through the use of liquid culture-based strategies could help facilitate the massive up-scaling of IPT required to reduce HIV and TB morbidity and mortality.

Development of low-cost inverted microscope to detect early growth of Mycobacterium tuberculosis in MODS culture

Background

The microscopic observation drug susceptibility (MODS) assay for rapid, low-cost detection of tuberculosis and multidrug resistant tuberculosis depends upon visualization of the characteristic cording colonies of Mycobacterium tuberculosis in liquid media. This has conventionally required an inverted light microscope in order to inspect the MODS culture plates from below. Few tuberculosis laboratories have this item and the capital cost of $5,000 for a high-end microscope could be a significant obstacle to MODS roll-out.

Methodology

We hypothesized that the precise definition provided by costly high-specification inverted light microscopes might not be necessary for pattern recognition.

Significance

In this work we describe the development of a low-cost artesenal inverted microscope that can operate in both a standard or digital mode to effectively replace the expensive commercial inverted light microscope, and an integrated system that could permit a local and remote diagnosis of tuberculosis.

Field and laboratory preparedness: challenges to rolling out new multidrug-resistant tuberculosis diagnostics

OBJECTIVES

In a pilot implementation project of the microscopic-observation drug-susceptibility methodology, we conducted a process evaluation to identify health system and logistic challenges that need to be addressed in order to harness the benefits of rolling out promising new diagnostic tools for multidrug-resistant tuberculosis (MDRTB).

METHODS

Regional data relating to health system practices and performance related to the MDRTB diagnostic algorithm were collected at health center, local, and regional laboratories.

RESULTS

Parallel implementation of a new test and an existing method creates demands on funds, personnel, sample transport, and information systems in addition to new test startup costs. Obviating the need for primary culture at intermediate laboratories through direct drug susceptibility testing (DST) at the regional reference laboratory significantly reduces delay. Field application of well-defined national guidelines for DST is patchy. If fidelity to national guidelines were perfect, DST requests would increase more than 50-fold, with important implications for laboratory capacity.

CONCLUSIONS

Implementing a new MDRTB diagnostic presents challenges to the laboratory environment, the existing DST process, and the application of national guidelines in peripheral clinics. Assessing each element can maximize efficient use of a new tool. Specifically, strengthening systems for transferring samples to the laboratory and delivering results to the requesting clinic in addition to investing in personnel and laboratory resources are integral to harnessing the benefits of high-performance new diagnostic tests and can bring added value to other programs in the health care system.

Upper-room ultraviolet light and negative air ionization to prevent tuberculosis transmission

BACKGROUND

Institutional tuberculosis (TB) transmission is an important public health problem highlighted by the HIV/AIDS pandemic and the emergence of multidrug- and extensively drug-resistant TB. Effective TB infection control measures are urgently needed. We evaluated the efficacy of upper-room ultraviolet (UV) lights and negative air ionization for preventing airborne TB transmission using a guinea pig air-sampling model to measure the TB infectiousness of ward air.

METHODS AND FINDINGS

For 535 consecutive days, exhaust air from an HIV-TB ward in Lima, Perú, was passed through three guinea pig air-sampling enclosures each housing approximately 150 guinea pigs, using a 2-d cycle. On UV-off days, ward air passed in parallel through a control animal enclosure and a similar enclosure containing negative ionizers. On UV-on days, UV lights and mixing fans were turned on in the ward, and a third animal enclosure alone received ward air. TB infection in guinea pigs was defined by monthly tuberculin skin tests. All guinea pigs underwent autopsy to test for TB disease, defined by characteristic autopsy changes or by the culture of Mycobacterium tuberculosis from organs. 35% (106/304) of guinea pigs in the control group developed TB infection, and this was reduced to 14% (43/303) by ionizers, and to 9.5% (29/307) by UV lights (both p < 0.0001 compared with the control group). TB disease was confirmed in 8.6% (26/304) of control group animals, and this was reduced to 4.3% (13/303) by ionizers, and to 3.6% (11/307) by UV lights (both p < 0.03 compared with the control group). Time-to-event analysis demonstrated that TB infection was prevented by ionizers (log-rank 27; p < 0.0001) and by UV lights (log-rank 46; p < 0.0001). Time-to-event analysis also demonstrated that TB disease was prevented by ionizers (log-rank 3.7; p = 0.055) and by UV lights (log-rank 5.4; p = 0.02). An alternative analysis using an airborne infection model demonstrated that ionizers prevented 60% of TB infection and 51% of TB disease, and that UV lights prevented 70% of TB infection and 54% of TB disease. In all analysis strategies, UV lights tended to be more protective than ionizers.

CONCLUSIONS

Upper-room UV lights and negative air ionization each prevented most airborne TB transmission detectable by guinea pig air sampling. Provided there is adequate mixing of room air, upper-room UV light is an effective, low-cost intervention for use in TB infection control in high-risk clinical settings.

Reducing the string test intra-gastric downtime for detection of Mycobacterium tuberculosis

OBJECTIVES

To explore the potential for reducing the procedural duration of the string test for the diagnosis of tuberculosis (TB) using microscopic observation drug susceptibility (MODS) culture.

METHODS

Twelve patients already diagnosed with pulmonary TB, four each with sputum smear acid-fast bacilli grade 1+, 2+ and 3+, underwent four consecutive string tests of varying intra-gastric downtime (IGDT) of 30 min, 1, 2 and 4 h. Each retrieved string was cut into three-one oesophageal and two gastric sections. Eluates from one of the gastric sections and the oesophageal section were cultured in MODS after a decontamination procedure; eluate from the other gastric section was cultured in MODS with no decontamination.

RESULTS

No significant difference was observed in the retrieval efficacy of Mycobacterium tuberculosis (P = 0.29) or time to positive MODS culture (P = 0.80) among string tests of varying IGDTs. Every patient with a sample that was positive after a 4-h IGDT also had positive culture of a 1-h IGDT sample. A pre-inoculation sample decontamination step significantly reduced culture contamination (P < 0.001).

CONCLUSION

In smear-positive patients, reducing the IGDT to 1 h did not affect the M. tuberculosis retrieval efficacy of the string test. Future evaluations in non-expectorating human immunodeficiency virus and paediatric populations should include a 1-h IGDT.

Can the power of mobile phones be used to improve tuberculosis diagnosis in developing countries?

The low-cost Microscopic Observation Drug Susceptibility (MODS) assay is a non-proprietary test that delivers rapid and accurate diagnosis of tuberculosis (TB) and multidrug-resistant TB. Although methodologically straightforward, implementation is challenging in isolated settings where personnel trained in plate reading are lacking. One affordable strategy to address this shortfall is the use of mobile phones, first to transmit images captured by an inverted microscope to a remote site where pattern recognition is performed by trained personnel, and second to receive the resulting output of this analysis. Such a system could be used for training of laboratory personnel through distance learning, resolution of equivocal appearances and quality assurance.

The infectiousness of tuberculosis patients coinfected with HIV

BACKGROUND

The current understanding of airborne tuberculosis (TB) transmission is based on classic 1950s studies in which guinea pigs were exposed to air from a tuberculosis ward. Recently we recreated this model in Lima, Perú, and in this paper we report the use of molecular fingerprinting to investigate patient infectiousness in the current era of HIV infection and multidrug-resistant (MDR) TB.

METHODS AND FINDINGS

All air from a mechanically ventilated negative-pressure HIV-TB ward was exhausted over guinea pigs housed in an airborne transmission study facility on the roof. Animals had monthly tuberculin skin tests, and positive reactors were removed for autopsy and organ culture for M. tuberculosis. Temporal exposure patterns, drug susceptibility testing, and DNA fingerprinting of patient and animal TB strains defined infectious TB patients. Relative patient infectiousness was calculated using the Wells-Riley model of airborne infection. Over 505 study days there were 118 ward admissions of 97 HIV-positive pulmonary TB patients. Of 292 exposed guinea pigs, 144 had evidence of TB disease; a further 30 were tuberculin skin test positive only. There was marked variability in patient infectiousness; only 8.5% of 118 ward admissions by TB patients were shown by DNA fingerprinting to have caused 98% of the 125 characterised cases of secondary animal TB. 90% of TB transmission occurred from inadequately treated MDR TB patients. Three highly infectious MDR TB patients produced 226, 52, and 40 airborne infectious units (quanta) per hour.

CONCLUSIONS

A small number of inadequately treated MDR TB patients coinfected with HIV were responsible for almost all TB transmission, and some patients were highly infectious. This result highlights the importance of rapid TB drug-susceptibility testing to allow prompt initiation of effective treatment, and environmental control measures to reduce ongoing TB transmission in crowded health care settings. TB infection control must be prioritized in order to prevent health care facilities from disseminating the drug-resistant TB that they are attempting to treat.

Pedestrian road traffic injuries in urban Peruvian children and adolescents: case control analyses of personal and environmental risk factors

Background

Child pedestrian road traffic injuries (RTIs) are an important cause of death and disability in poorer nations, however RTI prevention strategies in those countries largely draw upon studies conducted in wealthier countries. This research investigated personal and environmental risk factors for child pedestrian RTIs relevant to an urban, developing world setting.

Methods

This is a case control study of personal and environmental risk factors for child pedestrian RTIs in San Juan de Miraflores, Lima, Perú. The analysis of personal risk factors included 100 cases of serious pedestrian RTIs and 200 age and gender matched controls. Demographic, socioeconomic, and injury data were collected. The environmental risk factor study evaluated vehicle and pedestrian movement and infrastructure at the sites in which 40 of the above case RTIs occurred and 80 control sites.

Findings

After adjustment, factors associated with increased risk of child pedestrian RTIs included high vehicle volume (OR 7·88, 95%CI 1·97–31·52), absent lane demarcations (OR 6·59, 95% CI 1·65–26·26), high vehicle speed (OR 5·35, 95%CI 1·55–18·54), high street vendor density (OR 1·25, 95%CI 1·01–1·55), and more children living in the home (OR 1·25, 95%CI 1·00–1·56). Protective factors included more hours/day spent in school (OR 0·52, 95%CI 0·33–0·82) and years of family residence in the same home (OR 0·97, 95%CI 0·95–0·99).

Conclusion

Reducing traffic volumes and speeds, limiting the number of street vendors on a given stretch of road, and improving lane demarcation should be evaluated as components of child pedestrian RTI interventions in poorer countries.

Physician-initiated courtesy MODS testing for TB and MDR-TB diagnosis and patient management

SETTING

Laboratorio de Investigación de Enfermedades Infecciosas, Universidad Peruana Cayetano Heredia (UPCH) and government health centres, Lima, Peru.

OBJECTIVE

To evaluate the contribution of unselected (courtesy) microscopic observation drug susceptibility (MODS) testing to the diagnosis and/or drug susceptibility testing (DST) of tuberculosis and their subsequent impact upon patient management.

DESIGN

Retrospective database analysis and case note review of MODS culture-positive cases.

RESULTS

Mycobacterium tuberculosis was isolated in 28.9% of 225 samples (209 patients); 22.2% of 63 positive cases were multidrug-resistant. In 58 MODS culture-positive cases with follow-up data available, MODS provided culture confirmation of diagnosis, DST or both in 82.8%, before any standard method. In 41.4%, this result should have prompted a modification in patient management. Delays between laboratory result and initiation or change of treatment, where applicable, took on average 42 and 64 days, respectively, of which a delay of respectively 17 and 48 days occurred after the receipt of results by the health facility.

CONCLUSION

MODS provides important data for clinical management within a meaningful timeframe and should contribute positively to patient outcomes due to earlier initiation of appropriate therapy. Although clinicians may successfully select patients likely to benefit from MODS, ongoing work is required to identify optimal implementation of the assay and to reduce logistical and health system derived delays.

Improved diagnosis of pleural tuberculosis using the microscopic- observation drug-susceptibility technique

Tests for pleural tuberculosis are insensitive and expensive. We compared nonproprietary microscopic-observation drug-susceptibility (MODS) culture with Löwenstein-Jensen culture for evaluation of pleural specimens. MODS culture was associated with greatly increased diagnostic sensitivity and shorter time to diagnosis, compared with Löwenstein-Jensen culture (sensitivity of culture of biopsy specimens, 81% vs.51%; time to diagnosis, 11 days vs. 24 days; P < .001). The MODS technique is inexpensive, allows drug-susceptibility testing, and is a considerably improved diagnostic method for pleural tuberculosis.

Solar disinfection of MODS mycobacterial cultures in resource-poor settings

Introduction

Safe disposal of TB culture material in which the infectious burden of clinical samples has been greatly amplified is an important challenge in resource-limited settings. The bactericidal capacity of solar cookers has been demonstrated previously for conventional bacteria and contaminated clinical waste. We investigated the use of a simple solar cooker for the sterilization of mycobacterial broth cultures from the microscopic observation drug susceptibility assay (MODS).

Methods

Simulated TB culture materials were prepared by inoculating 24-well MODS plates with 500 µL of a known concentration of Mycobacterium bovis BCG. In a series of experiments, samples were simultaneously placed inside a box-type solar cooker and control box and removed at timepoints between 15 minutes and 6 hours. Quantitative cultures were performed using retrieved samples to determine sterilization effect.

Results

All cultures from the control box were positive at or within 1–4 logs of inoculation concentration. Simulated culture plates at concentrations from 10³colony-forming-units (CFU)/ml to 10⁷ CFU/ml were completely sterilized after only one hour of cooker exposure, at temperatures between 50–102°C. At 10⁹ CFU/ml (far in excess of diagnostic cultures), it was only possible to recover mycobacterial growth in plates removed after 15 minutes. By 30 minutes all plates were effectively sterilized.

Discussion

Solar disinfection provides a very effective, safe and low-cost alternative to conventional equipment used for disposal of mycobacterial culture material. Effect of climatic conditions and optimal operating procedure remain to be defined.