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First published online September 27, 2006
British Journal of Radiology (2007) 80, 302-306
© 2007 British Institute of Radiology
doi: 10.1259/bjr/15037569
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Full paper

Comparison of plain chest radiography and high-resolution CT in human immunodeficiency virus infected patients with community-acquired pneumonia: a sub-Saharan Africa study

K Nyamande, MBChB, FCP (SA), MD1, U G Lalloo, MD, FCCP, FRCP (London)1 and F Vawda, FC Rad (SA)2

Departments of 1 Medicine and 2 Radiology, Nelson R Mandela School of Medicine, University of KwaZulu-Natal, Durban, South Africa

Correspondence: Prof. Umesh Gangaram Lalloo, Internal Medicine, University of KwaZulu Natal, 719 Umbilo Road, Congella, Durban, KwaZulu Natal, 4013 South Africa. E-mail: lalloo{at}ukzn.ac.za


   Abstract
Top
 Abstract
Introduction
 Patient recruitment and methods
 Statistical analysis
 Results
 Discussion
 References
 
The objective of the study was to determine the proportion of patients with missed lesions on plain chest radiographs compared with high-resolution computed tomography (HRCT) in 49 human immunodeficiency virus (HIV) infected patients with community-acquired pneumonia (CAP). Patients underwent plain chest radiography and HRCT scans of the chest at admission. Microbiological investigations for CAP were performed. An experienced radiologist, without knowledge of clinical or pathological data, reported the chest radiographs and HRCT scans. The study group included 26 females and 23 males, aged 18–53 years (mean age 36 years). Organisms were isolated from 26 patients (53%). In 40 patients (82%), the HRCT scans demonstrated lesions not visualized on the plain chest radiographs. There was 100% correlation between plain radiographic and HRCT scan findings in nine cases (18%). Lesions that were not visualized on the plain radiographs but elucidated on HRCT included: pleural effusion (n = 14), ground-glass opacification (n = 20), pericardial effusion (n = 8), cavitation (n = 4), cysts (n = 4), bullae (n = 4), abscess (n = 1) and pneumothorax (n = 1). In 20 of 23 cases, hilar lymphadenopathy, identified on HRCT, was not recognized on plain chest radiographs. In patients in whom an organism was isolated, a correct HRCT diagnosis of pulmonary tuberculosis, bacterial pneumonia and Pneumocystis carinii pneumonia (PCP) was made in 80%, 84% and 100% of cases, respectively. The proportion of patients with missed lesions on plain chest radiographs in HIV infected patients with CAP was high. This has important implications for management and prognosis. HRCT scans correlate well with the microbiological diagnosis when reported by an experienced radiologist.


   Introduction
Top
 Abstract
 Introduction
Patient recruitment and methods
 Statistical analysis
 Results
 Discussion
 References
 
Sub-Saharan Africa has the largest number of human immunodeficiency virus (HIV) infected subjects worldwide. The HIV pandemic in the region is still increasing and has not yet reached a plateau. The number of HIV infected patients presenting with pulmonary infections has also increased dramatically.

The imaging technique of choice in patients with clinical symptoms and signs of community-acquired pneumonia (CAP) has traditionally been the chest radiograph [1–7]. This is largely because chest radiography is easy to perform, widely accessible, cheap and associated with low radiation. High-resolution CT (HRCT) scanning is reserved for the analysis of complex cases, particularly when the chest radiograph is equivocal with regard to associated central obstruction, cavitation, lymphadenopathy, or empyema [8, 9]. The role of HRCT, however, is rapidly evolving. In febrile neutropenic patients, CT scanning is more sensitive than plain film in early detection of lung infections [10]. HRCT may have a role in patients whose chest radiographs are non-revealing or non-diagnostic [11]. HRCT is helpful in the differential diagnosis of infectious from non-infectious acute parenchymal disease in the immunocompetent patient, but is of limited value in making a specific diagnosis [12].

There are no studies from sub-Saharan Africa on the utility and value of HRCT scanning of the chest in HIV infected patients with CAP. We compared HRCT with plain chest radiography, and the usefulness of HRCT in the microbiological diagnosis of PCP, pulmonary tuberculosis and bacterial CAP. We hypothesized that, in HIV infected patients presenting with CAP, clinically important lesions may not be evident on plain chest radiography.


   Patient recruitment and methods
Top
 Abstract
 Introduction
 Patient recruitment and methods
Statistical analysis
 Results
 Discussion
 References
 
The study was performed at King Edward VIII Hospital, Durban, South Africa. This is a tertiary teaching hospital of the Nelson R Mandela School of Medicine. The hospital serves a predominantly black African population from the townships of Umlazi, KwaMashu, Inanda, Clermont and Chesterville. The ethics committee of Nelson R Mandela School of Medicine, Durban, South Africa, granted permission to perform the study. From June 2000 to July 2001, 54 patients were recruited into the study. All the patients were black Africans. They were randomly selected from inpatients presenting with symptoms and signs of CAP with a chest radiograph showing consolidation or an infiltrate compatible with the diagnosis. None of the patients was on antiretroviral therapy. Microbiological tests performed following induction and expectoration of sputum included Gram stain and culture, and Ziel–Neelsen stain for acid-fast bacilli. Blood cultures and urine tests for Legionella pneumophila and Streptococcus pneumoniae were performed. The PCP immunofluorescence test was performed on induced sputum to detect Pneumocystis jirovecii. CD4 counts were assessed by flow cytometry.

A HRCT scan of the chest was performed after admission to the medical ward, consisting of 1.5 mm collimation sections at 10 mm intervals reconstructed with a high spatial frequency algorithm. All scans were performed without intravenous contrast medium at suspended end-inspiration with the patient in a supine position. Scans were reviewed at a setting appropriate for both lung parenchyma and mediastinum. The chest radiographs and HRCT scans were evaluated by a radiologist who had no prior knowledge of the aetiology of the pneumonia, duration of symptoms, severity of symptoms, degree of dyspnoea, presence or absence of fever or leukocytosis. The HRCT scans were reported without the concurrent availability of the chest radiographs.

Evaluated HRCT findings included consolidation, ground-glass opacification, nodular opacification, pleural effusions, pericardial effusions, abscess formation, cavitation, bullae, cysts, mediastinal lymphadenopathy (nodes greater than 1 cm in short axis diameter) and the presence or absence of a pneumothorax. The radiologist was asked to record the most likely aetiological diagnosis as bacterial pneumonia, Mycobacterium tuberculosis, Pneumocystis jirovecii pneumonia or any other diagnosis. The chest radiographic and HRCT scan findings were then compared.


   Statistical analysis
Top
 Abstract
 Introduction
 Patient recruitment and methods
 Statistical analysis
Results
 Discussion
 References
 
Two by two tables were used to calculate the sensitivity, specificity and positive and negative predictive values of HRCT diagnosis vs the microbiological diagnosis.


   Results
Top
 Abstract
 Introduction
 Patient recruitment and methods
 Statistical analysis
 Results
Discussion
 References
 
Of the 54 patients recruited into the study 5 were excluded because they were HIV seronegative. Thus data from 49 patients were analysed. There were 26 females and 23 males. The mean age of the patients was 36 years (range 18–53 years). The CD4 count was determined in 37 patients. The mean CD4 count was 184 cells µl–1 (range 0–1223 cells µl–1).

The findings on chest radiography correlated with the HRCT scan findings in only nine patients (18%). In 40 patients (82%), abnormalities were missed on the chest radiograph, with a total of 76 missed lesions. The most commonly missed abnormalities included ground-glass opacification (50% of patients) and mediastinal lymphadenopathy (50% of patients), followed by pleural effusions (35% of patients) and pericardial effusions (20% of patients) (Table 1Go). Analysis of the missed lesions as a proportion of the total number (n = 76) revealed that 26% were mediastinal lymphadenopathy, 26% ground-glass opacification, 18% pleural effusions, 10% pericardial effusions, 5% cavitation, 5% bullae, 5% cysts and 1% abscess formation and pneumothorax.


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  		Table 1. Lesions missed on plain chest radiography

 
Microbiology
There was a total of 31 isolates from 26 patients (53%). No organisms were isolated in the remainder (Table 2Go). The most common organism isolated was Mycobacterium tuberculosis (32%), followed by Streptococcus pneumoniae (29%) and PCP (19%). Five patients had polymicrobial pneumoniae. Other organisms isolated were Escherichia coli (2), Gram-negative bacilli (2), Klebsiella pneumoniae (1), Haemophilus influenzae (1) and Staphylococcus pneumoniae (1). A correct HRCT diagnosis of pulmonary tuberculosis, bacterial pneumonia and pneumocystis carinii pneumonia (PCP) was made in 80%, 84% and 100% of cases, respectively (Table 3Go). The sensitivities of HRCT compared with microbiology for the diagnosis of pulmonary tuberculosis, PCP and bacterial pneumonia were 80%, 100% and 85%, respectively. However, HRCT was not specific for any diagnosis compared with microbiology (Tables 3Go).


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  		Table 2. Organisms isolated in 26 of the 49 patients

 

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  		Table 3. Radiologist's HRCT scan diagnosis vs microbiological diagnosis

 

   Discussion
Top
 Abstract
 Introduction
 Patient recruitment and methods
 Statistical analysis
 Results
 Discussion
References
 
Few studies have been performed on the role of HRCT scanning of the chest in HIV related pulmonary infections [13–21]. None of these studies have been from sub-Saharan Africa, which currently has the highest HIV or acquired immunodeficiency syndrome burden. Most have focused on PCP [13, 15, 16, 19, 20]. To our knowledge, only Diehl et al [21] from Germany have investigated the clinical value of HRCT of the chest in patients with known HIV infection and acute lung disease, but the entry criteria were that of a normal or non-specific chest radiograph. In our study, no patients with normal chest radiographs were recruited. No patients with normal chest radiographs had HRCT scans performed.

Our study has shown that in HIV infected African patients with CAP, an alarmingly high percentage of patients (82%) have abnormalities that are not visible on plain chest radiograph. This study supports the findings of Guillemi et al [17], who undertook a study to characterize the frequency of lung lesions in asymptomatic HIV infected individuals with advanced disease. All were homosexual males on assessment for initiation of PCP prophylaxis. The results of their study demonstrated that as many as 60% of HIV infected patients have unexpected abnormalities on HRCT at the time of starting PCP prophylaxis. Syrjala et al [22] compared HRCT with chest radiography in 47 immunocompetent patients with signs and symptoms of CAP. HRCT identified all 18 cases apparent on chest radiography as well as an additional 8 cases.

The superiority of HRCT is well recognized [12, 23–25]. Superior contrast resolution and cross-sectional display is achieved. HRCT not only improves characterization of parenchymal infections in terms of location and extent of disease, but also surpasses chest radiography in the detection of complications [24]. The present study demonstrated the sensitivity of HRCT in detailing abnormalities not apparent on chest radiography in a cohort of HIV infected patients with CAP.

Mediastinal lymphadenopathy, ground-glass opacification, pleural effusions and pericardial effusions were among the most commonly missed lesions on chest radiographs. Lack of identification of these abnormalities may impact significantly on patient management and clinical outcome. The detection of some abnormalities may expand the options available to the clinician for obtaining diagnostic specimens for microbiology and histology. The attending physician had knowledge of the HRCT findings. The HRCT findings in conjunction with the clinical features aided the physician in commencing therapy in patients in whom microbiological tests were negative. The HRCT findings did not direct the microbiological investigations as most tests were performed within the shortest possible time on admission. Some abnormalities contribute to significant morbidity and may increase mortality. Bullae and cysts may rupture causing a spontaneous pneumothorax. Over time, these lesions may enlarge, compressing normal lung in patients already afflicted with the ravages of HIV induced pulmonary infections such as repeated bacterial pneumonia, PCP and tuberculosis. A small pneumothorax may rapidly expand causing compression of already diseased lung with consequent demise of a patient. A lung abscess not treated for the appropriate duration may increase morbidity and mortality.

The present study reflects the presence of significant complications detected on HRCT scans in patients with advanced HIV disease. The mean CD4 count in the present study group was 184 cells µl–1 and the lowest was zero. Advanced disease, as determined by the CD4 count, is associated with HRCT abnormalities even in asymptomatic patients [17]. The lower the CD4 count, the greater the likelihood of both opportunistic and non-opportunistic pulmonary infections. Co-infections become common. Coinfections occurred in 20% of patients (5 out of 26) in the present study.

The sensitivity of HRCT diagnosis compared with the microbiological diagnosis was 100% for PCP, 85% for bacterial pneumonia and 80% for tuberculosis. The present study confirmed that no HRCT or chest radiographic pattern is specific for any infection [7, 26–28]. The average positive predictive values attained in the present study suggest that HRCT scans are relatively good for screening in, but not for screening out. The negative predictive values that were obtained in the present study suggest that the technique cannot be used to exclude PCP, tuberculosis, or bacterial CAP.

Radiologists rely on the clinical information provided to come to a reasonably accurate differential diagnosis. In the absence of clinical information it is difficult to distinguish pneumonia and other pathological processes [29]. Although the radiologist in the present study was blinded to patients' clinical information, correlation with the microbiological diagnosis was good, as shown by the high sensitivities obtained. In patients who are not improving clinically, HRCT may assist with the decision to switch therapy. However, the limitations of HRCT in the management of HIV associated CAP need to be recognized. Sub-Saharan countries are poor and under-resourced. There are financial, technical, human resource and logistical constraints.

In conclusion, we have shown that a large proportion of HIV infected African patients presenting with CAP have clinically important abnormalities on HRCT that are not apparent on plain chest radiographs. This has important implications for the management of HIV associated CAP. When reported by an experienced radiologist, the HRCT scan diagnosis has good correlation with the microbiological diagnosis. This may be useful in modifying or switching therapy.

This study was funded by a grant from the Medical Research Council of South Africa.


   Acknowledgments
 
We would like to thank Chandrika Vedalankar, Department of Medicine, Nelson R Mandela School of Medicine, University of KwaZulu-Natal, for secretarial assistance; the Department of Microbiology, Nelson R Mandela School of Medicine, University of KwaZulu-Natal, for analysis of microbiological specimens; and Tonya Esterhuizen of Biostatistics for the statistical analysis.

Received for publication March 29, 2006. Revision received July 21, 2006. Accepted for publication August 15, 2006.


   References
Top
 Abstract
 Introduction
 Patient recruitment and methods
 Statistical analysis
 Results
 Discussion
 References
 

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