Tuberculosis is one of humankind’s oldest infections but, unlike many other microbial foes, Mycobacterium tuberculosis remains prevalent. By one estimate, a third of the world’s population is infected, and the traditional rule is that every one of these people will transmit the disease to 20 others by coughing out infected respiratory secretions. One result is an estimated 1.8 million deaths annually. 1
Severe acute respiratory syndrome (SARS), on the other hand, is new, caused by a previously unknown coronavirus that appears to have originated in animals. 2 SARS was first identified in the Guangdong Province of Southern China late in 2002. Like tuberculosis, it is spread by respiratory droplets. With today’s large numbers of travelers and immigrants, the disease required little time to spread around the world. Within a few months, more than 8,000 people had been infected, 3 of whom more than 900 died. 2
For both diseases, high-risk populations can be identified; this is an important factor in developing screening programs. For example, people infected by HIV and those with lung diseases (such as silicosis) are particularly vulnerable to tuberculosis infection if exposed. 4-6 Although the incidence of tuberculosis is low and declining in the US population, 7 prisoners 8 and intravenous drug users 9 also remain at high risk. In addition, the high prevalence of infection in much of the world means that many immigrants can pose a threat, particularly to employees of the US Bureau of Immigration and Customs Enforcement. For SARS, many cases were acquired in health care facilities via contact with people whose infection status was not understood. 10 The forced reliance on chest radiography for diagnosis placed radiology department staff at particular risk. 11
The traditional method of screening for tuberculosis was to obtain a medical history and perform a physical examination plus a skin purified protein derivative (PPD) test that was read 2 to 3 days later. The skin test, however, has high false-negative and false-positive rates. As many as half of people with active (transmissible) tuberculosis have negative skin tests. The high false-positive rate meant that when a PPD test given by what was then the US Immigration and Naturalization Service (INS) was positive, a mobile radiography provider came to the facility to obtain confirmatory chest films that then had to taken elsewhere to be developed and read. An average of 7 to 10 days passed before a diagnosis was available.
Beginning in 1999, the INS began to use chest radiography as their primary screening method and sought a means of obtaining and reading large numbers of studies quickly. The service contracted with DIANAssociates, Inc, of Severna Park, Md, to establish a network based on Swissray’s direct digital radiography (ddR) equipment.
|Philip A. Templeton, MD|
Philip A. Templeton, MD, founder and CEO of Templeton Technologies of Severna Park and former chair of the radiology department at the University of Maryland, was part of this project from the beginning. He describes the results of the new approach, saying, “Today, detainees at INS centers are fingerprinted and then stand in front of the C-arm of a digital detector. A button is pushed and, within about a minute, the images have been transmitted on a secure private network to the University of Maryland Medical System, as well as to archiving facilities. If the image is not idealand it is not always ideal, given the conditions under which it was obtainedit can be manipulated on the workstation to fix it. The detainee does not have to be kept there until someone approves the image. The radiologist reviews the images and generates an automatic electronic report that returns within seconds to the provider’s site and to the archives. If the study is positive, the radiologist also calls the referring center to make sure that they know.”
Templeton continues, “The bottom line is that we shortened a 7-day to 10-day turnaround time to a maximum of 4 hours. With conventional equipment, you could not get the results this quickly if you had people standing by the processor waiting for films to come out and running them over to the radiologist to be read.”
Hundreds of films are read per day (every day, around the clock). The Division of Immigrant Health Services reports that about 150 cases of active tuberculosis are spotted each year. 12 Infected detainees remain in custody for treatment, which is monitored to ensure patient compliance and success in eradicating the disease, as recommended by the Advisory Council for the Elimination of Tuberculosis. “Even if the detainees are going back to their own countries, we treat them to stop the spread of tuberculosis there,” Templeton says. “They may also try to return to the United States.”
SOUTH AFRICAN MINES
Miners are at high risk of infectious respiratory diseases because of their confinement in large groups in small spaces. In South Africa, by law, all of the roughly 100,000 miners must be imaged when they begin and end employment, and at least once a year during their employment, to screen for tuberculosis and silicosis or other occupational lung disease, depending on the type of mine. By government mandate, these films must be kept for 40 years.
Traditionally, this screening was done using mass miniature radiography or conventional radiography. The first method, which uses 10×10-cm plates, is cheap but inaccurate, identifying only about 22% of people known to be infected with tuberculosis and overlooking silicosis entirely, according to information provided by Gerhard Breytenbach, of Xeikona Medical Solutions, Johannesburg, South Africa, which specializes in installing digital medical imaging solutions. It also entails a high radiation dose (the deep dose from a single study can exceed 26 mSv), a worrisome feature given the frequency with which miners must be imaged. As a result of these drawbacks, the Radiation Board of the South African Department of Health wants this equipment phased out; adding to the difficulty, it is old and can no longer be repaired if it breaks.
Conventional radiography with 35×43-cm plates is somewhat more accurate, catching about 32% of confirmed cases, but it does not satisfy the current South African government demand for 75% accuracy. The deep radiation dose is 0.34 mSv, although a miner’s exposure may be higher in that approximately 4% of the studies have to be retaken to obtain interpretable films. To avoid the extra exposure and speed up the scanning of large numbers of people, films of questionable quality sometimes were accepted, a practice that no doubt contributed to the unsatisfactory accuracy rate.
With both types of equipment, the requirement for 40-year film retention created significant demands for expensive, fireproof storage space. Even then, it could not be fulfilled, as standard films gradually deteriorate, usually becoming unreadable within 10 years.
Swissray ddR systems began to be installed in the mines on February 1, 2004. These mines have realized several benefits. The systems are fast: for example, at one of the platinum mines, in the past, an entire day was required to screen all 370 miners. Since ddR was installed, a screening session that starts at 7 am can be completed by 11:30 am. Another benefit is that fully trained technologists are not needed to obtain satisfactory images. A training course developed at Capetown University prepares radiology clerks within 1 or 2 days; they are then fully qualified to obtain lung images.
Of even greater importance is that the ddR systems are more accurate than the previous technology. The use of ddR has improved detection accuracy by 280%, according to information provided by Xeikona Medical Solutions. The ddR examinations also identify many cases of silicosis and lesions such as pulmonary plaques that were not seen with previous equipment. Contributing to accuracy is the ability of the equipment to recall the exposure parameters used for each miner’s previous studies, thereby reducing irrelevant differences between images. Less-than-perfect images can also be adjusted electronically to improve their diagnostic quality, as a result of which the retake rate has been only 1.5%, according to information provided by Xeikona. Even this rate is expected to decline with experience; most of the inadequate films are caused by incorrect patient positioning or improper breath holding. The ability to correct images and to review them immediately for adequacy means that miners need not wait for confirmation that their studies are satisfactory. In the past, the need for retakes and the required waiting until good images had been obtained sometimes caused a miner to miss a shift.
All of the mines have excellent telecommunications infrastructure and can communicate over high-speed links, making it possible to send images elsewhere for review, if necessary. Aurum Health, Johannesburg, South Africa, a participant in the screening system, is working with the University of Chicago to develop a computer-aided detection system for tuberculosis, which should make film interpretation faster.
The deep radiation dose from a ddR system is only about 0.23 mSv, according to information provided by Xeikona, a fact that persuaded one of the largest South African mining companies, AngloGold Ashanti, to participate in a program of twice-a-year tuberculosis screening. The practice has paid off, according to information from Xeikona, which installed the ddR systems: the mortality rate for tuberculosis has been reduced by more than half with the more frequent examinations.
The ddR systems have produced several cost savings. First, there are no consumables such as film, developing chemicals, and film sleeves. Second, electricity use has been reduced to about 21% of the previous amount, and no water is needed. Third, office staff members do not spend time carrying films around, filing them, or hunting for them. Fourth, large fireproof storage areas are not required. Fifth, there is no chemical waste to be disposed of after film processing.
Breytenbach notes an unexpected benefit of the ddR systems. “When a miner is found to have tuberculosis, he must go to the hospital; he cannot go back to the mine,” Breytenbach explains. “To keep earning money, he may send a brother, cousin, or somebody else to the hospital in his place and return to work. He can continue to spread the infection, and the right person is not being treated. Since we have installed the digital equipment, where you can see the previous image right beside the current image, it has become more difficult for people to get away with this. The first time it happened, the man in front of the ddR had situs inversus: his heart was on the wrong side! When they displayed the previous image, they knew immediately that it was not the same guy. Several other cases have been found since, although they were not so dramatic.”
Clearly, pulmonary disease screening has become much easier with the advent of ddR . The Chinese government has purchased Swissray ddR systems to help it control SARS. Other applications for this fast, accurate, and easy-to-use equipment seem certain to appear in the next few years.
Judith Gunn Bronson, MS, is a contributing writer for Decisions in Axis Imaging News.
- Iademarco MF, Castro KG. Epidemiology of tuberculosis. Semin Respir Infect. 2003;18:225-240.
- Lapinsky SE, Granton JT. Critical care lessons from severe acute respiratory syndrome. Curr Opin Crit Care. 2004;10:53-58.
- Groneberg DA, Zhang L, Welte T, Zabel P, Chung KF. Severe acute respiratory syndrome: global initiatives for disease diagnosis. QJM. 2003;96:845-852.
- Aaron L, Saadoun D, Calatroni I, et al. Tuberculosis in HIV-infected patients: a comprehensive review. Clin Microbiol Infect. 2004;10:388-398
- Cahn P, Perez H, Ben G, Ochoa C. Tuberculosis and HIV: a partnership against the most vulnerable. J Int Assoc Physicians AIDS Care. 2003;2:106-123.
- Eisler R. Health risks of gold miners: a synoptic review. Environ Geochem Health. 2003;25:325-345.
- Trends in tuberculosis–United States, 1998-2003 [published correction appears in: MMWR Morb Mortal Wkly Rep. 2004;53:246]. MMWR Morb Mortal Wkly Rep. 2004;53:209-214.
- Reichard AA, Lobato MN, Roberts CA, Bazerman LB, Hammett TM. Assessment of tuberculosis screening and management practices of large jail systems. Public Health Rep. 2003;118:500-507.
- Perlman DC, Friedmann P, Horn L, et al. Impact of monetary incentives on adherence to referral for screening chest x-rays after syringe exchange-based tuberculin skin testing. J Urban Health. 2003;80:428-437.
- McDonald LC, Simor AE, Su IJ, et al. SARS in healthcare facilities, Toronto and Taiwan. Emerg Infect Dis. 2004;10:777-781.
- Tsou IY, Goh JS, Kaw GJ, Chee TS. Severe acute respiratory syndrome: management and reconfiguration of a radiology department in an infectious disease situation. Radiology. 2003;229:21-26.
- Post-detention completion of tuberculosis treatment for persons deported or released from the custody of the Immigration and Naturalization Service–United States, 2003. MMWR Morb Mortal Wkly Rep. 2003;52:438-441.