INT J TUBERC LUNG DIS 16(10):1354–1357 © 2012 The Union http://dx.doi.org/10.5588/ijtld.12.0174 E-published ahead of print 2 August 2012
SHORT COMMUNICATION
Diagnostic yield of tuberculosis using sputum induction in HIV-positive patients before antiretroviral therapy S. D. Lawn,*† A. D. Kerkhoff,*‡ P. Pahlana,* M. Vogt,* R. Wood* * The Desmond Tutu HIV Centre, Institute for Infectious Disease and Molecular Medicine, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa; † Department of Clinical Research, Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK; ‡ George Washington University School of Medicine and Health Sciences, Washington DC, USA SUMMARY
Adults (n = 602) enrolling in a South African antiretroviral treatment clinic underwent culture-based screening for tuberculosis (TB), regardless of symptoms. For those unable to spontaneously expectorate a ‘spot’ sample (n = 124), sputum induction with nebulised hypertonic saline was used to obtain a first sample and also to rapidly obtain a second sample from all patients. Collection of both samples typically took 10–15 min. The preva-
lence of culture-positive TB was 15.6% (95%CI 12.8– 18.8). Spontaneously expectorated spot samples yielded 79.8% of all culture-positive TB diagnoses. The incremental yield from those needing an induced first sample was 5.3% and the yield from induced second samples was 14.9%. K E Y W O R D S : HIV; tuberculosis; screening; diagnosis; Africa; sputum induction; antiretroviral
TUBERCULOSIS (TB) is a leading cause of morbidity and mortality in antiretroviral treatment (ART) services in sub-Saharan Africa,1 and much of this disease at baseline remains unascertained under routine programme conditions.2 The high burden of disease in these often overcrowded clinical services also presents a substantial risk of nosocomial transmission. Intensified case finding is therefore a key intervention, permitting early diagnosis and rapid initiation of treatment.2 Studies from South Africa have found that approximately 15–25% of patients without a pre-existing TB diagnosis enrolling in ART services have sputum culture-positive TB.3–5 In view of such a high TB prevalence and the limited sensitivity of symptom screening, it has been suggested that all patients in the highest prevalence settings should be screened for TB using appropriate microbiological tests.2–5 However, case finding among patients with advanced human immunodeficiency virus (HIV) associated immune suppression presents a major challenge.2 Sputum samples from patients accessing ART often contain very low numbers of organisms, as reflected by negative smears, high rates of disease that are negative on Xpert® MTB/RIF testing (Cepheid, Sunnyvale, CA, USA) and prolonged time to positivity in liquid culture.2,6 Sputum quality is therefore likely to be an important factor in making diagnoses. Gastric washings and fibreoptic bronchsocopy are invasive procedures that may help obtain samples for micro-
biological testing. However, evidence suggests that simple nebulised sputum induction with hypertonic saline is as effective as these techniques,7,8 and yet is non-invasive and can be performed in out-patient settings. The incremental value of this approach for screening ambulatory patients in ART services in sub-Saharan Africa at a single out-patient clinic visit, however, is unknown. We have conducted studies of novel TB diagnostics in patients enrolling in an ART service in Cape Town, South Africa, using culture as a gold standard.5,9 This provided the opportunity for us to examine the utility of sputum induction. We were able to determine 1) the proportion of additional TB cases diagnosed through use of sputum induction among patients who were unable to spontaneously expectorate a first spot sputum sample, and 2) the incremental yield of a second sample of sputum obtained immediately after the first using nebulised sputum induction.
METHODS The ART service in Gugulethu Township, Cape Town, has previously been reported in detail, as has the major burden of TB within this service.10 Details of patient recruitment and laboratory procedures are described in the parent studies.5,6,9 Eligible patients were new patients referred to the ART clinic aged >18 years, ART-naïve and with no current TB diagnosis.
Correspondence to: Stephen D Lawn, Desmond Tutu HIV Centre, Institute of Infectious Disease and Molecular Medicine, Faculty of Health Sciences, University of Cape Town, Anzio Road, Observatory 7925, Cape Town, South Africa. Tel: (+27) 21 650 6970. Fax (+27) 21 650 6963. e-mail:
[email protected] Article submitted 2 March 2012. Final version accepted 20 April 2012.
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All participants provided written informed consent. The study was approved by the research ethics committees of the University of Cape Town, Cape Town, South Africa, and the London School of Hygiene & Tropical Medicine, London, UK. Patients were prospectively recruited and investigated at their first clinic visit. Demographic details were recorded and a standardised symptom-screening questionnaire was completed. Two sputum samples were requested from each patient: a spontaneously expectorated spot specimen was obtained first, followed by a second that was induced using 3% hypertonic saline administered via an ultrasonic nebuliser (Medel S.p.A., San Polo di Torrile, Italy). If a spot sputum could not be expectorated spontaneously, then an attempt was made to obtain both by sputum induction. The study nurse provided patients with careful instructions, supervised sputum collection and ensured as far as possible that samples were from the lower respiratory tract and not the oral cavity, by questioning and visual inspection. Both samples were typically obtained within a 10–15 min time-frame. Sampling was performed in a small sputum ‘booth’ built onto the clinic, but separated by an air-tight door and with open lattice brick-work walls that provided privacy but allowed excellent ventilation.
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Laboratory procedures have been described elsewhere.5,9 In brief, samples were decontaminated, concentrated by centrifugation and cultured using Mycobacteria Growth Indicator Tube (MGIT™; BD, Sparks, MD, USA) incubated for up to 6 weeks. TB cases were defined by culture of Mycobacterium tuberculosis.
RESULTS Of 602 patients enrolled, the median age was 33.8 years, 67% were female and the median CD4 cell count was 168 cells/μl (interquartile range [IQR] 95–232). A total of 94 sputum culture-positive TB diagnoses were made, giving an overall TB prevalence of 15.6% (95% confidence interval [CI] 12.8– 18.8) and a prevalence of 17.4% (95%CI 14.3–20.9) among those with sputum samples. Twenty-seven cases (28.7%) were smear-positive. TB cases had a median CD4 cell count of 129 cells/μl (IQR 51–204); 78 (83%) had a positive World Health Organization symptom screen, 64 (68%) reported having current cough (any duration) and 25 (27%) reported cough lasting ⩾2 weeks. The proportions of spot #1, induced #1 and induced #2 samples (Figure 1) testing culture-positive were respectively 15.7% (95%CI 12.5–19.3; 75/478),
Figure 1 Flow diagram showing sputum samples obtained and the incremental yield of culture-positive TB diagnoses arising from induced samples. A total of 94 culture-positive cases were detected, of which 27 were smear-positive. TB = tuberculosis.
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The International Journal of Tuberculosis and Lung Disease
8.1% (95%CI 2.7–17.8; 5/62) and 13.0% (95%CI 10.2–16.3; 67/514). Overall, 3.2% of the cultures were contaminated, but this was not related to sample type. We then analysed the incremental yield of the different sputum sample categories. A spot sputum sample was produced by 478 (79.4%) patients; these samples yielded 75 (79.8%) of 94 total culture-positive TB diagnoses (Figure 1). Of 124 (20.6%) patients who could not produce a spot sputum sample, only half (n = 62) were able to produce a sample following sputum induction, yielding a further five cases (5.3% of total diagnoses). A total of 460 patients produced first sputum samples that were culture-negative (403 spot + 57 induced; Figure 1). A second sample was obtained from 431 (93.7%) of these using sputum induction, yielding an additional 14 culture-positive diagnoses (11 in patients with a negative spot sputum first sample and three in patients with a negative induced sputum first sample). These comprised 14.9% of overall diagnoses. The overall yield of TB diagnoses from the different sputum sample categories and according to patient symptoms is summarised in Figure 2. This shows that the yield of TB diagnoses would be markedly reduced had only those patients with symptoms been investigated. Regardless of patient symptom category, there was an incremental yield of TB cases using sputum induction (Figure 2).
Figure 2 The incremental yield of culture-positive TB diagnoses from induced sputum samples in patients categorised according to symptoms. Proportions are shown using the total number of culture-positive TB cases (n = 94) as the denominator throughout. The incremental yield of induced samples is shown over and above the yield derived from spontaneously expectorated spot sputum samples. TB = tuberculosis; WHO = World Health Organization.
DISCUSSION There was a high prevalence of sputum culture-positive TB in this cohort (15.6% overall and 17.4% of patients who produced sputum samples). There is a critical need to efficiently obtain sputum samples to permit rapid and accurate TB diagnosis in this clinical context in view of the high morbidity, mortality and risk of nosocomial TB transmission.2 The collection of two sputum samples at a single clinic visit presents considerable advantages, and it has been proposed that this be performed 1 h apart for ‘same-day’ or ‘front-loaded’ smear microscopy.11 In our study, all patients were screened, regardless of symptoms, and two samples were obtained for culture typically within just 10–15 min. Sputum induction for those who could not produce a spot sample and rapidly obtaining an additional second sample from all patients was extremely efficient, making clinic work-flow streamlined and minimising patient time in the clinic. Sputum induction enabled eight TB diagnoses (8.4% of the total yield) to be made in patients who could not produce a spot specimen and 11 (11.7% of the total yield) TB diagnoses to be made in patients whose first spot samples were culture-negative (Figure 1). Thus, overall, 20.2% of all cases and 14.8% of smear-positive cases were made from induced sputum samples. Importantly, sputum induction provided useful incremental diagnostic yield, regardless of clinical symptoms at the time of screening (Figure 2). Of note, the use of molecular strain typing in diagnostics studies in this clinic has found no evidence of crosscontamination arising in either the clinic environment during sputum collection or in the laboratory.4,6 The proportion of samples testing culture-positive was a little lower among induced second samples (13.0%) than in spontaneously expectorated spot samples (15.7%), and may reflect clearance of the highest yield sputum from the airways with the first sample. Despite this, the incremental yield of the second sample (n = 14, 14.9%) was similar to the incremental yield of MGIT culture of a second sputum sample in a study of HIV-infected patients in Thailand, in which patients were required to return to the clinic on the next day with a morning sample.12 Use of sputum induction may permit high-quality samples to be obtained rapidly, without the need for the patient to return the next day. Of the 403 patients whose spot sputum samples were culture-negative, we do not know what proportion might have been able to spontaneously expectorate a second sample and what the yield of these samples would have been. We can thus only conclude from this study that sputum induction enabled very efficient collection of two sputum samples and that sputum induction increased the yield by between 8 and 19 cases (8.5–20.2%; Figure 1). The use of efficient sputum collection in this way and used in
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combination with rapid molecular diagnostics, such as the Xpert MTB/RIF assay, considerably accelerates TB diagnosis in this clinical setting.9 Randomised trials of different strategies and cost-effectiveness analyses are needed.
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Acknowledgements The authors thank the staff of the Hannan Crusaid ART clinic. SDL was funded by the Wellcome Trust, London, UK. RW was funded in part by National Institutes of Health grants RO1 A1058736-01A1 and 5UO1A1069519-02, and United States Agency for International Development grant 3UO1A1069924-O2S.
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References 1 Lawn S D, Harries A D, Anglaret X, Myer L, Wood R. Early mortality among adults accessing antiretroviral treatment programmes in sub-Saharan Africa. AIDS 2008; 22: 1897–1908. 2 Lawn S D, Wood R. Tuberculosis in antiretroviral treatment services in resource-limited settings: addressing the challenges of screening and diagnosis. J Infect Dis 2011; 204 (Suppl 4): S1159–S1167. 3 Bassett I V, Wang B, Chetty S, et al. Intensive tuberculosis screening for HIV-infected patients starting antiretroviral therapy in Durban, South Africa. Clin Infect Dis 2010; 51: 823– 829. 4 Lawn S D, Edwards D J, Kranzer K, Vogt M, Bekker L G, Wood R. Urine lipoarabinomannan assay for tuberculosis screening before antiretroviral therapy diagnostic yield and association with immune reconstitution disease. AIDS 2009; 23: 1875–1880. 5 Lawn S D, Kerkhoff A D, Vogt M, Wood R. Diagnostic accu-
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racy of a low-cost, urine antigen, point-of-care screening assay for HIV-associated pulmonary tuberculosis before antiretroviral therapy: a descriptive study. Lancet Infect Dis 2012; 12: 201–209. Lawn S D, Kerkhoff A D, Vogt M, Ghebrekristos Y, Whitelaw A, Wood R. Characteristics and early outcomes of patients with Xpert MTB/RIF-negative pulmonary tuberculosis diagnosed during screening before antiretroviral therapy. Clin Infect Dis 2012; 54: 1071–1079. Brown M, Varia H, Bassett P, Davidson R N, Wall R, Pasvol G. Prospective study of sputum induction, gastric washing and bronchoalveolar lavage for the diagnosis of pulmonary tuberculosis in patients who are unable to expectorate. Clin Infect Dis 2007; 44: 1415–1420. Gonzalez-Angulo Y, Wiysonge C S, Geldenhuys H, et al. Sputum induction for the diagnosis of pulmonary tuberculosis: a systematic review and meta-analysis. Eur J Clin Microbiol Infect Dis 2012; 31: 1619–1630. Lawn S D, Brooks S V, Kranzer K, et al. Screening for HIVassociated tuberculosis and rifampicin resistance before antiretroviral therapy using the Xpert MTB/RIF Assay: a prospective study. PLoS Med 2011; 8: e1001067. Lawn S D, Myer L, Bekker L G, Wood R. Burden of tuberculosis in an antiretroviral treatment programme in sub-Saharan Africa: impact on treatment outcomes and implications for tuberculosis control. AIDS 2006; 20: 1605–1612. Hirao S, Yassin M A, Khamofu H G, et al. Same-day smears in the diagnosis of tuberculosis. Trop Med Int Health 2007; 12: 1459–1463. Monkongdee P, McCarthy K D, Cain K P, et al. Yield of acidfast smear and mycobacterial culture for tuberculosis diagnosis in people with human immunodeficiency virus. Am J Respir Crit Care Med 2009; 180: 903–908.
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RÉSUMÉ
Les adultes (n = 602) recrutés pour un traitement antirétroviral dans un dispensaire d’Afrique du Sud ont subi un dépistage de la tuberculose (TB) basé sur la culture quels que soient leurs symptômes. Chez les sujets incapables d’expectorer de façon spontanée un échantillon sur le terrain (n = 124), on a utilisé la provocation de l’expectoration par des aérosols de solution saline hypertonique afin d’obtenir un premier échantillon ainsi que pour obtenir rapidement une deuxième échantillon chez
l’ensemble des patients. Le prélèvement des deux échantillons a pris typiquement de 10 à 15 min. La prévalence des cultures positives pour la TB a été de 15,6% (IC95% 12,8–18,8). Les échantillons spontanément expectorés sur le terrain ont fourni 79,8% de l’ensemble des diagnostics de TB à culture positive. Le rendement supplémentaire chez ceux exigeant un premier échantillon provoqué a été de 5,3% et le rendement des deuxièmes échantillons provoqués a été de 14,9%. RESUMEN
Se llevó a cabo una detección sistemática de la tuberculosis (TB) en los adultos que se inscribían en un consultorio de tratamiento antirretrovírico en Suráfrica (n = 602), independientemente de la presencia de síntomas respiratorios. En las personas que no lograban una expectoración espontánea inmediata (n = 124) se practicó una nebulización con solución salina hipertónica, a fin de inducir una primera muestra de esputo y además obtener rápidamente una segunda muestra de todos los
pacientes. En general, la recogida de ambas muestras tomó de 10 a 15 min. La prevalencia de cultivos positivos para Mycobacterium tuberculosis fue 15,6% (IC95% 12,8 a 18,8). Las muestras de esputo inmediatas obtenidas espontáneamente dieron lugar al 79,8% de todos los diagnósticos de TB con cultivo positivo. El incremento del rendimiento con una primera muestra inducida fue del 5,3% y con la segunda muestra inducida fue del 14,9%.
