The influence of dose and N-acetyltransferase-2 (NAT2) genotype and phenotype on the pharmacokinetics and pharmacodynamics of isoniazid

OBJECTIVE

This study evaluated the pharmacokinetics of isoniazid (INH) associated with optimal early bactericidal activity (EBA), defined as 90% of the maximum EBA (EBA(90)) and the influence of N-acetyltransferase-2 (NAT2) subtype on the ability of pulmonary tuberculosis (PTB) patients to reach the identified pharmacokinetic values after INH doses ranging from 0.2 to 10-12 mg/kg body weight.

METHODS

INH serum concentrations and NAT2 subtype were determined during four studies of PTB patients in three of whom the EBA of INH was determined. The relationship of EBA to area under the curve (AUC) (AUC(0-infinity)) and 2-h serum concentrations was examined by exponential regression and fitted curves estimated the AUC(0-infinity) and 2-h serum concentrations at which EBA(90) was reached.

RESULTS

EBA(90) was reached at an AUC(0-infinity) of 10.52 microg/ml per hour and 2-h serum concentrations of 2.19 microg/ml. An AUC(0-infinity) of 10.52 microg/ml per hour was reached by all 66 patients receiving a 10-12 mg/kg INH dose and all 21 receiving 6 mg/kg, except 1 of 10 (10%) homozygous fast (FF) acetylators; however, at 5 mg/kg, 4 of 12 (33%) FF and 26 of 27 (96%) heterozygous fast (FS), but all 21 homozygous slow (SS) acetylators did so; and 1 of 3 (33%) FF, 2 of 6 (33%) FS, but all 4 SS acetylators at dose 3 mg/kg. An INH 2-h serum concentration of 2.19 microg/ml was reached by all 66 patients receiving 10-12 mg/kg and all 21 receiving 6 mg/kg, except for 2 (20%) FF acetylators at a dose of 5 mg/kg; however, only 3 (25%) of 12 FF acetylators, but 26 (96%) of 27 FS acetylators, and all 21 SS acetylators reached this concentration; and at a dose of 3 mg/kg, 1 (33%) of 3 FF acetylators, 2 (33%) of 6 FF, but all 4 SS acetylators.

CONCLUSIONS

At a 6 mg/kg dose, all except a minority of FF NAT2 acetylators, achieve an INH AUC(0-infinity) and 2-h INH serum concentrations associated with EBA(90), as did all 4 SS acetylators receiving 3 mg/kg. Any dose reduction below 6 mg/kg body weight will tend to disadvantage a significant proportion of faster acetylators, but, conversely, SS acetylators require only a 3 mg/kg dose to achieve a satisfactory exposure to INH.

Radionuclides in fruit systems: model prediction-experimental data intercomparison study

This paper presents results from an international exercise undertaken to test model predictions against an independent data set for the transfer of radioactivity to fruit. Six models with various structures and complexity participated in this exercise. Predictions from these models were compared against independent experimental measurements on the transfer of 134Cs and 85Sr via leaf-to-fruit and soil-to-fruit in strawberry plants after an acute release. Foliar contamination was carried out through wet deposition on the plant at two different growing stages, anthesis and ripening, while soil contamination was effected at anthesis only. In the case of foliar contamination, predicted values are within the same order of magnitude as the measured values for both radionuclides, while in the case of soil contamination models tend to under-predict by up to three orders of magnitude for 134Cs, while differences for 85Sr are lower. Performance of models against experimental data is discussed together with the lessons learned from this exercise.

Radionuclides in fruit systems: model-model intercomparison study

Modeling is widely used to predict radionuclide distribution following accidental radionuclide releases. Modeling is crucial in emergency response planning and risk communication, and understanding model uncertainty is important not only in conducting analysis consistent with current regulatory guidance, but also in gaining stakeholder and decision-maker trust in the process and confidence in the results. However, while methods for dealing with parameter uncertainty are fairly well developed, an adequate representation of uncertainties associated with models remains rare. This paper addresses uncertainty about a model's structure (i.e., the relevance of simplifying assumptions and mathematical equations) that is seldom addressed in practical applications of environmental modeling. The use of several alternative models to derive a range of model outputs or risks is probably the only available technique to assess consistency in model prediction. Since each independent model requires significant resources for development and calibration, multiple models are not generally applied to the same problem. This study uses results from one such model intercomparison conducted by the Fruits Working Group, which was created under the International Atomic Energy Agency (IAEA) BIOMASS (BIOsphere Modelling and ASSessment) Program. Model-model intercomparisons presented in this study were conducted by the working group for two different scenarios (acute or continuous deposition), one radionuclide ((137)Cs), and three fruit-bearing crops (strawberries, apples, and blackcurrants). The differences between models were as great as five orders of magnitude for short-term predictions following acute radionuclide deposition. For long-term predictions and for the continuous deposition scenario, the differences between models were about two orders of magnitude. The difference between strawberry, apple, and blackcurrant contamination predicted by one model is far less than the difference in prediction of contamination for a single plant species given by different models. This study illustrates the importance of problem formulation and implementation of an analytic-deliberative process in risk characterization.

Monitoring the ingestion of anti-tuberculosis drugs by simple non-invasive methods

This investigation retrospectively assessed inexpensive non-invasive qualitative methods to monitor the ingestion of anti-tuberculosis drugs isoniazid, rifampicin and rifapentine. Results showed that commercial test strips detected the isoniazid metabolites isonicotinic acid and isonicotinylglycine as efficiently as the isonicotinic acid method in 150 urine samples. The presence of rifamycins in urine samples (n=1085) was detected by microbiological assay techniques and the sensitivity compared to the n-butanol extraction colour test in 91 of these specimens. The proportions detected by the two methods were significantly different and the sensitivity of the n-butanol procedure was only 63.8% (95% CL 51.2-76.4%) as compared to that of the superior microbiological method. Final validation (n=691) showed that qualitative assays measure isoniazid and rifamycin ingestion with an efficiency similar to high-performance liquid chromatography. The qualitative procedures may therefore be valuable in clinical trials and in tuberculosis clinics to confirm drug ingestion.

Rethinking undergraduate curricula: A Delphi study of human resource management and industrial and organisational psychology

The aim of this qualitative study is to bring clarity to the confusion about the interconnectedness, similarities and differences between the fields of Human Resource Management (HRM) and Industrial and Organisational Psychology (I&OP), for the purposes of curriculum development. The Delphi technique was used to gather data from 13 participants (five international and eight national). Analysis was done interpretively using Atlas.ti. Results indicate that HRM and I&OP are distinct but interrelated fields of study and can therefore be presented in separate but interrelated undergraduate curricula. Opsomming Die doel van die kwalitatiewestudie is om duidelikheid te verkry oor die verwarring rakende die interverwantskap, ooreenkomste en verskille tussen die velde van Menslike Hulpbronbestuur (MHB) en Bedryfs- en Organisasie Sielkunde vir die doeleindes van kurrikulumontwikkeling. Die Delphi tegniek is gebruik om data van 13 deelnemers (vyf internasionaal en agt nasionaal) te versamel. Ontleding is op ’n interpreterende wyse gedoen deur gebruik te maak van Atlas.ti. Die resultate toon dat MHB en Bedryfs- en Organisasie Sielkunde onderskeibare, maar verbandhoudende studievelde is en daarom aangebied kan word in afsonderlike, maar interverwante voorgraadse kurrikula.

The effect of confidence and method of questioning on eyewitness testimony

Very often eyewitnesses are perceived as being accurate due to the confidence in the accuracy of their own testimony. The confidence displayed by an eyewitness may possibly be increased by the method of questioning used by legal professionals and police. The present study examines the confidence-accuracy relationship and the effect the method of questioning (open-ended versus closed-ended questions) may have on the confidence of eyewitnesses. The sample of 412 respondents consisted of scholars (11 to 14-year-olds), university students, the public and Police College students. A significant relationship between memory accuracy and confidence was found for more than 70% of the questions. Closed-ended questions provided a significantly higher rate of accuracy than open-ended questions. A significantly larger proportion of respondents to the closed-ended questions were more confident about their answers than those who responded to the open-ended questions.

Method of questioning and the accuracy of eyewitness testimony

System variables are integrally part of factors that can be controlled by the legal system to enhance the accuracy of testimony by eyewitnesses. Apart from examining the relationship between questioning as system variable and the accuracy of testimony, the present study furthermore explores the relationship between type of questioning and certain biographical variables (occupation, age, gender and race). To achieve the aim of the study, 412 respondents consisting of 11 to 14-year-olds, university students, the public and Police College students participated and were exposed to open-ended or closed-ended questions. It was found that the participants who responded to the closed-ended questions were significantly more accurate than those who answered the open-ended questions. All the biographical groups, except the public, were more accurate in responding to the closed-ended questions. The scholars obtained the lowest scores (although not always significant) for both the open-ended and closed-ended questions. With respect to age the 18 to 25-year-olds obtained significantly higher scores than the other groups for the closed-ended questions. Whites performed significantly better than blacks in response to the open-ended and closed-ended questions.

Modelling and experimental studies on the transfer of radionuclides to fruit

Although fruit is an important component of the diet, the extent to which it contributes to radiological exposure remains unclear, partially as a consequence of uncertainties in models and data used to assess transfer of radionuclides in the food chain. A Fruits Working Group operated as part of the IAEA BIOMASS (BIOsphere Modelling and ASSessment) programme from 1997 to 2000, with the aim of improving the robustness of the models that are used for radiological assessment. The Group completed a number of modelling and experimental activities including: (i) a review of experimental, field and modelling information on the transfer of radionuclides to fruit; (ii) discussion of recently completed or ongoing experimental studies; (iii) development of a database on the transfer of radionuclides to fruit; (iv) development of a conceptual model for fruit and (v) two model intercomparison studies and a model validation study. The Group achieved significant advances in understanding the processes involved in transfer of radionuclides to fruit. The work demonstrated that further experimental and modelling studies are required to ensure that the current generation of models can be applied to a wide range of scenarios.

Radionuclide migration in forest ecosystems--results of a model validation study

The primary objective of the IAEA's BIOMASS Forest Working Group (FWG) was to bring together experimental radioecologists and modellers to facilitate the exchange of information which could be used to improve our ability to understand and forecast radionuclide transfers within forests. This paper describes a blind model validation exercise which was conducted by the FWG to test nine models which members of the group had developed in response to the need to predict the fate of radiocaesium in forests in Europe after the Chernobyl accident. The outcomes and conclusions of this exercise are summarised. It was concluded that, as a group, the models are capable of providing an envelope of predictions which can be expected to enclose experimental data for radiocaesium contamination in forests over the time scale tested. However, the models are subject to varying degrees of conceptual uncertainty which gives rise to a very high degree of divergence between individual model predictions, particularly when forecasting edible mushroom contamination. Furthermore, the forecasting capability of the models over future decades currently remains untested.

The Influence of Human N-Acetyltransferase Genotype on the Early Bactericidal Activity of Isoniazid

The elimination of isoniazid is subject to the influence of the N-acetyltransferase 2 (NAT2) genotype, and individuals may be homozygotic slow, heterozygotic fast, or homozygotic fast acetylators of isoniazid. The early bactericidal activity (EBA) of an antituberculosis agent can be determined by quantitative culture of Mycobacterium tuberculosis in sputum samples obtained from patients with pulmonary tuberculosis during the first days of treatment. In these studies, the EBA of isoniazid during the first 2 days of treatment was determined for 97 patients with sputum smear-positive pulmonary tuberculosis following isoniazid doses of < or =37.5 mg, 75 mg, 150 mg, 300 mg, and 600 mg. The NAT2 genotype was determined in 70 patients, and the association between EBA and genotype was examined in this subgroup. Similarly, the relationship between EBA and isoniazid serum concentration was evaluated in 87 patients. The mean EBA of isoniazid increased with dose, but it levelled off between doses of 150 mg (mean EBA, 0.572) and 300 mg (mean EBA, 0.553). Significant differences were found in the mean EBA of isoniazid between the homozygous slow acetylator group and the heterozygous fast acetylator group and between the homozygous slow acetylator group and the homozygous fast acetylator group, but not between the heterozygous fast acetylator group and the homozygous fast acetylator group. The EBA appeared to reach a maximum at a 2-h isoniazid concentration of 2-3 microg/mL. These data confirm a significant effect of NAT2 genotype on the EBA of isoniazid over a range of doses.

Critical Competencies To Promote A Customer Service Core Capability In A Human Resources Call Centre

In today’s information-intensive environment customer service is an important aspect that differentiates one organisation from another. This research focuses on those individual competencies which will lead to a customer service core capability in a Human Resources Call Centre. Data was obtained from Call Centre agents (n=18), supervisors (n=3) and customers (n=25) by means of five focus group-, three individual- and 25 telephonic interviews, respectively. The transcendental realism research procedure was applied within a qualitative research paradigm. Ten key competencies were identified by all groups of participants. Opsomming In vandag se inligtings-intensiewe omgewing is kliëntediens ’n belangrike aspek wat organisasies van mekaar onderskei. Hierdie navorsing fokus op welke individuele bevoegdhede tot ’n kliëntedienssleutelbekwaamheid in ’n Menslikehulpbron-oproepsentrum sal lei. Data is van Oproepsentrumagente (n=18), -toesighouers (n=3) en -kliënte (n=25) ingewin deur middel van onderskeidelik vyf fokusgroep-, drie individuele- en 25 telefoniese onderhoude. Die transendentale realisme navorsingsprosedure is binne ’n kwalitatiewe navorsingsparadigma toegepas. Tien sleutelbevoegdhede is deur al drie groepe deelnemers geïdentifiseer.

Early bactericidal activity of antituberculosis agents

The early bactericidal activity (EBA) of an antituberculosis agent is arbitrarily defined as the fall in log(10) colony forming units (cfu) of Mycobacterium tuberculosis per ml sputum per day during the first 2 days of treatment. Determining the EBA is an important preliminary step in the clinical evaluation of an antituberculosis agent. We review the results of eight published studies of the EBA of different antituberculosis agents, the impact of these results on our understanding of the actions of the respective agents, the clinical characteristics and sputum findings of patients included in these studies, and explore sources of variation in the EBA results. Patients in these studies had a mean age of 31-36 years, a mean weight of 50-57 kg, 67% were male and 56% had lung involvement covering an area of more than one lung, and 90% had multicavitary disease. None of these findings were related to EBA in any study. The mean log(10) cfu per ml sputum in the first specimen was 6.474. This was related to radiological extent of disease and cavity size in one study (p < 0.001) and, in the case of isoniazid to EBA with a rise in EBA of 0.094 (95% CL 0.029-0.158) for each tenfold rise in cfu counts/ml sputum. The overall variation in EBA in these studies was 0.0303, that due to laboratory processing of specimens was 0.0011, and due to patient characteristics and sputum sampling 0.0212. The EBA is a reproducible investigation that has contributed significantly to our knowledge of the actions and characteristics of both established and new antituberculosis agents. The greatest source of variation in EBA results appears to be that due to interpatient variation in disease characteristics and sputum sampling.

The effect of violent versus non-violent incidents on eyewitness memory

As South Africans are daily subjected to violent incidents for which they are summoned to testify about in court, months or years after the event in question occurred, it is of importance to determine the effect violence has on memory after an extended period of time. The present study not only aimed to determine the accuracy of short-term and long-term memory after exposure to a violent and non-violent incident, but also the relationship between short-term and long-term memory and different biographical variables (occupation, age, gender and race). Four-hundred-and-seventy-four respondents consisting of university students, the business sector and Police College students participated and were divided into a short-term and long-term memory group. After a five to six week retention period a significant decrease in the accuracy scores for both the violent and non-violent incident occurred. Significant higher average scores for all the biographical groups in the short-term memory group in comparisons with the long-term memory groups were obtained.

The relationship between memory and the recall of specific details

When eyewitnesses are exposed to an event, certain details tend to capture their attention more than other details, which ensures the better recall of the details that were observed. As little research has focussed on the relationship between certain biographical variables (occupation, age, gender, race and retention period) and specific event details, the present study attempts to shed some light on this area. A sample of 295 participants was obtained from 12- to 14-year-olds, university students, the public and Police College students that were divided into a short-term and long-term memory group. The details that were focussed on in the questionnaire were divided into obvious physiognomic, less pronounced physiognomic, clothing, circumstantial, and action-related details. Between the short-term and long-term memory groups it was found that significant differences were indicated for only certain items related to obvious physiognomic details, clothing details, circumstantial evidence and action-related details. For all the different biographical groups significant differences were found for certain items belonging to the different groups of details.

Memory accuracy of a real-life simulated incident

Due to an awareness that both laboratory and real-life research present limitations, the present study attempts to combine the two research approaches, making use of the strengths of both methodologies. A real-life situation was created in a classroom and combined with laboratory conditions to determine the influence of certain variables (occupation, age, gender, race and retention interval) on the accuracy of eyewitness reporting. A total of 295 participants consisting of 12- to 14-year-olds, University students, the public and Police College students were divided into a short- and long-term memory group. The short-term group were assessed immediately after witnessing the incident, while the long-term group were only assessed five to six weeks later. It was found that the effect of passage of time was insubstantial; however, the performance of the short-term group had already been disconcertingly poor. The school children did not perform significantly less well than other occupational groups, and the members of the Police did not perform significantly better than the other groups. No significant differences were found for the different gender and racial groups.

A randomized controlled study of the impact of dietary zinc supplementation in the management of children with protein-energy malnutrition in Lesotho. II: Special investigations

Protein-energy malnutrition (PEM) remains one of the common causes of morbidity and mortality among children throughout the world. The supplementation of 10 mg elemental zinc, as zinc sulphate, was evaluated in the management of PEM in a randomized, controlled, double-blind clinical trial in 300 children, aged 6-60 months (zinc, n = 150; control, n = 150) admitted to the Queen Elizabeth II Hospital, Maseru, Lesotho. Supplementation and follow-up were done for 3 months post-discharge from the hospital. Both the supplemented and the control groups presented with biochemically determined zinc deficiency on presentation. Despite supplementation the treated group only began to show evidence of biochemical increase in serum zinc at 60 days post-discharge from hospital. This may represent the period of replacement of the total body zinc. Zinc deficiency was more severe in those children in the control group that died after admission to hospital than those that survived, suggesting that low serum levels in children with PEM are associated with a poor prognosis. Zinc did not emerge as a predicator of poor prognosis in the supplemented group as very few children died in this group. The supplemented group also made significant gains as far as albumin levels were concerned, which probably reflects rehabilitation of their malnutrition. The associated improvement in haematological parameters has not been described before and may be secondary to the decreased burden of disease in the supplemented group. These findings suggest that not only were significant benefits of zinc supplementation shown for morbidity in mortality of children in Lesotho with PEM, but these trends were also demonstrated on biochemical profiles.

A randomized controlled study of the impact of dietary zinc supplementation in the management of children with protein-energy malnutrition in Lesotho. I: Mortality and morbidity

Protein-energy malnutrition (PEM) remains one of the common causes of morbidity and mortality among children throughout the world. The supplementation of 10 mg elemental zinc, as zinc sulphate, was evaluated in the management of PEM in a randomized, controlled double-blind clinical trial in 300 children, aged 6-60 months (zinc, n = 150; control, n = 150) admitted to the Queen Elizabeth II Hospital, Maseru, Lesotho. Supplementation and follow-up were done for 3 months post-discharge from the hospital. Mortality during hospitalization was significantly lower in the zinc supplemented group (4.7 per cent), compared with 16.7 per cent in the control group. The prevalence of morbidity was significantly higher in the control group at 1, 2, and 3 month's follow-up. In the zinc supplemented group 58 per cent of the children were above the 80th percentile of expected weight-for-age 3 months after discharge, compared with 27.6 per cent in the control group. Dietary zinc supplementation resulted in a significant reduction in diarrhoeal disease, respiratory morbidity, and episodes of clinical anaemia, skin infections, and fever as well as vomiting in children with PEM. These findings suggest that interventions to improve zinc intake in their management may be of benefit to Basotho children in Lesotho with PEM.

The early bactericidal activity of streptomycin

SETTING

Patients with sputum smear-positive, newly diagnosed pulmonary tuberculosis studied at Tygerburg Hospital, Cape Town, for their early response to streptomycin (SM).

OBJECTIVE

To determine the standard early bactericidal activity (EBA), namely the fall in viable counts of tubercle bacilli in 16-hour sputum collections during the first 2 days of treatment with SM.

DESIGN

Patients were randomised to logarithmically spaced daily doses of 7.5, 15 or 30 mg/kg SM. A comparison by standard biological assay methods was then made with previous estimations of the EBA of paromomycin in doses of 7.5 and 15 mg/kg.

RESULTS

An EBA of 0.133 obtained with 30 mg/kg SM differed significantly from zero (P = 0.0009), while the EBAs of 0.043 with 15 mg/kg and -0.025 with 7.5 mg/kg did not so differ. A linear regression equation of EBA = -0.2587 + 0.2627 log10 dose was obtained with significant slope (P = 0.007). Paromomycin was estimated to be 1.745 more potent than SM with wide 95% confidence limits (0.6-28.6), indicating that it cannot be considered more potent than SM.

CONCLUSIONS

The low EBAs show that SM has low, dose-related, bactericidal activity in cavities, consistent with results from clinical trials. If streptomycin-resistant bacilli are present, paromomycin is probably the aminoglycoside of choice.

Children with intellectual disability in rural South Africa: prevalence and associated disability

The objective of the present study was to determine the prevalence of intellectual disability (ID) and its associated disabilities in rural South African children aged 2-9 years. It was undertaken in eight villages in the district of Bushbuckridge, Northern Province, South Africa. A two-phase design was utilized. The first phase involved screening children on a house-to-house basis by interviewing mothers or caregivers using an internationally validated questionnaire for detecting childhood disability in developing countries. The second phase consisted of a paediatric/neurodevelopmental assessment of the children who screened positive. A total of 6692 children were screened; 722 (10.8%) had a paediatric evaluation and 238 children were diagnosed with ID, giving a minimum observed prevalence of 35.6 per 1000 children in this population. The prevalence of severe and mild ID was 0.64 per 1000 and 29.1 per 1000 children, respectively. The male:female ratio of children with ID was 3:2. In the affected children, a congenital aetiology for the ID was determined in 49 subjects (20.6%), an acquired aetiology in 15 (6.3%) and the aetiology was undetermined in 174 children (73.1%). Epilepsy (15.5%) and cerebral palsy (8.4%) were the commonest associated disabilities. The present study represents the first data on the prevalence of ID and associated disabilities in rural South African children. The prevalence of ID was comparable with results from a study performed in one other African country (Zambia) as well as those from other developing countries. The data provide an initial factual insight into ID and its associated disabilities for healthcare, social service and educational policy planners. This study provides a basis for the initiation and development of appropriate and integrated services for the best possible care of individuals affected with these disabilities, and for their possible prevention.

Early bactericidal activity of amoxicillin in combination with clavulanic acid in patients with sputum smear-positive pulmonary tuberculosis

The early bactericidal activity (EBA) of an antituberculosis agent is the rate of decrease in viable colony-forming units (CFU) per milliliter of sputum during the first 2 d of treatment of patients with previously untreated smear-positive pulmonary tuberculosis. The objective of this open randomized study was to evaluate the EBA of the combination of amoxicillin 3 g and clavulanic acid 750 mg. Ten patients with a mean age of 34 y and a mean weight of 56 kg received amoxicillin/clavulanic acid and 5 patients with a mean age of 34 y and a mean weight of 57 kg received no drug. In the patients receiving 1 dose of amoxicillin/clavulanic acid daily for 2 d the mean log10CFU/ml of sputum before treatment was 6.7402 (SD 0.539) and after 2 d of treatment 6.7046 (SD 0.609); the corresponding values in patients receiving no drug were 6.7823 (SD 0.563) and 6.7502 (SD 0.673), respectively. The EBA of 0.018 (SD 0.130) in patients receiving amoxicillin/clavulanic acid did not differ significantly from that of 0.016 (SD 0.069) in patients receiving no drug. It is unlikely that the combination of amoxicillin/clavulanic acid has an important place in the treatment of tuberculosis with the exception of those patients with multidrug-resistant tuberculosis who are otherwise therapeutically destitute.

The early bactericidal activity of a low-clearance liposomal amikacin in pulmonary tuberculosis

The early bactericidal activity (EBA) of a liposomal preparation of amikacin (MiKasome) with a long plasma half-life of 120-200 h was examined in seven patients with newly diagnosed, smear-positive pulmonary tuberculosis. Liposomal amikacin was given in slow iv infusions of 30 mg total amikacin/kg body weight on three successive days. Cfu counts were set up on 16 h sputum collections preceding the first dose and following each dose and were used for calculating the EBA. Despite the high concentrations of total amikacin, >1000 mg/L, obtainable in plasma, no evidence of EBA was obtained. In view of the considerable activity of liposomal amikacin in experimental murine tuberculosis, this finding indicates that liberation of amikacin from the long-life liposomes occurs only in macrophages that are not usually present in the vicinity of the large extracellular clumps of bacilli in the cavity caseum.