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Infectiousness of air from a tuberculosis ward: ultraviolet irradiation of infected air: comparative infectiousness of different patients
R E V I E W S A N D C O M M E N T S AT A G L A N C E The field of infection surveillance, prevention, and control is rooted in a rich history that has been documented for well over a century. The first two reviews address the topics of John Snow's work on cholera and Richard Riley's classic studies of tuberculosis and guinea pigs. These articles were published before the establishment of formal programs in hospital epidemiology, but they have been referred to repeatedly through the years as models for ways to address the control of infectious diseases. Florence Nightingale's mortality statistics from the mid-19th century are presented as an example of the importance of appropriate data collection and analysis for surveillance. With the advent of pressures in health care to generate "rates" for everything, readers will find this cautionary tale particularly useful. During the early part of the 20th century, many rituals and practices were developed as a result of nursing beliefs about transmission of infectious agents. Double-bagging of trash and linen, among the most well-known of these rituals, was not studied scientifically until the 1980s; both of these studies on double-bagging are reviewed. Perhaps the most important disease complex to influence infection prevention and control practices in this century is HIV infection and AIDS. The first description of patients with AIDS is reviewed here, with comments about where we have been and may go in the future with HIV and AIDS. Finally, antibiotics have played a major role in the control of infections for the past 50 years. A review of the past, present, and future of antimicrobial agents completes the section.
Leland S. Rickman, MD Marguerite McMillan Jackson, RN, PhD University of California San Diego Medical Center
The cholera near Golden Square Snow d. Excerpted from: Snow d. Snow on cholera. Cambridge (MA): Harvard University Press, 1949.
This classic descriptive epidemiologic study provides an important example for current studies. In it, Snow describes his experience during a 1-month p e r i o d with a cholera epidemic in London. The goal of the study was to determine the source of the outbreak and prevent further spread of the disease. He took a methodical approach to the investigation, beginning by determining when the outbreak began by obtaining a list of deaths from cholera in a 1-week period. After determining the exact day of the outbreak, he then plotted the location of each death on a m a p to determine where the disease began and h o w far it had spread. After noticing a cluster of infections around the Broad Street pump, he interviewed several persons who lived in the area to determine the attack rate among those who drank from the well. The outbreak was determined to be point-source in nature, and Snow r e c o m m e n d e d the removal of the p u m p to limit the spread of cholera. After the removal of the p u m p handle, the incidence of cases dropped dramatically. Several epidemiologic tools were used beneficially in this study. Examples include the epidemiologic curve, the spot map, and the attack rate. These techniques are still used by infection conAJIC Am J Infect Control 1997;25:65-9. Copyright © 1997 by the Association for Professionals in Infection Control and Epiderniology, Inc. 0196-6553/97
$5.00 + 0
17/51/78612
trol professionals to specify the time, place, and persons involved in an outbreak. Snow's methods were enhanced by his thorough investigation. By examining all aspects of the outbreak, he was able to determine the source of the outbreak, as well as the mode of transmission. The only limitation to this study is the fact that most of the residents fled the area when the outbreak reached its peak. Whether removal of the p u m p handle in itself significantly decreased the attack rate will never be known. Although Snow's investigation occurred more than a century ago, his study remains the basis for m o d e m outbreak investigations, from small clinics to the largest metropolitan hospitals. A n d r e w C. Zau
MPH Student Graduate School of Public Health San Diego State University
A e r i a l d i s s e m i n a t i o n of p u l m o n a r y t u b e r c u l o s i s : a t w o - y e a r s t u d y of c o n t a g i o n in a t u b e r c u l o s i s w a r d Riley RL, Mills CC, Nyka W, Weinstock N, Storey PB, Sultan LU, et al. Am J Hyg 1959;70:185-96.
I n f e c t i o u s n e s s of a i r f r o m a t u b e r c u l o s i s w a r d : u l t r a v i o l e t i r r a d i a t i o n of i n f e c t e d air: c o m p a r a t i v e i n f e c t i o u s n e s s of different patients Riley RL, Mills CC, O'Grady F, Sultan LU, Wittstadt F, Shivpuri DN. Am Rev Respir Dis 1962;85:511-25.
We take for granted h o w the infectivity of certain diseases have been elucidated. When people sneezed in the Middle Ages, the words "God bless you" were not to express sympathy for one's immediate health, but to offer hope against losing one's soul. Although it was generally believed that 65
AJIC 66
Reviews
tuberculosis was spread by the air passages (Keers RY, Rigden BG, Yound FH. Pulmonary tuberculosis. Livingstone: Edinburgh, 1945:43-54), it was not until Riley and coworkers published these two landmark studies that the aerosol infectivity of Mycobacterium tuberculosis was firmly established. In one study, the investigators constructed an air-ventilation system in which air flowed from the ward rooms of patients with active pulmonary tuberculosis to a separate, distant r o o m containing guinea pigs. The guinea pigs, housed in cages, were arranged in a grid. All cages received equal air flow. To prevent other sources of tuberculosis infection, including cross-infection among the guinea pigs, the cage floors were made of wire mesh and contained no bedding material. The guinea pigs underwent monthly tuberculin skin tests. Maintenance personnel were also periodically screened with skin tests. Of 373 guinea pigs that were housed in the cages during a 2-year period, 77 were found to react to the tuberculin skin test, and tuberculous infection was found in 71 after they were killed. Primary pulmonary tuberculosis was found in 51 of the 71 guinea pigs. Guinea pigs were not believed to infect each other, because the distribution of infections did not differ significantly from chance and the guinea pigs that had tuberculin reactions were removed before they were believed to be infectious. The drug-sensitivity spectra of M. tuberculosis were almost identical between isolates from the sputum of patients with tuberculosis and isolates obtained from the autopsies of guinea pigs who reacted to the tuberculin skin tests when the respective patients were present. In another study, these investigators provided further evidence that tuberculosis was transmitted by air by showing that infectivity was eliminated with UV irradiation. UV irradiation had previously b e e n s h o w n to sterilize aerosol microbes (Riley RL, Wells WF, Mills CC, Nyka W, McLean RL. Air hygiene in tuberculosis: quantitative studies of infectivity and control in a pilot ward. Am Rev Tuberc 1957;75:420-31.). Air flow was directed from the wards of patients with pulmonary tuberculosis to two separate rooms by w a y of air ducts. The rooms contained cages that housed guinea pigs. Air flow to one of the guinea pig rooms underwent UV irradiation; the other r o o m received untreated air. Only guinea pigs w h o received u n t r e a t e d air acquired tuberculosis. Guinea pigs that breathed irradiated air did not acquire tuberculosis. Again, the experimenters
February 1997
were able to determine which patients were most infectious on the basis of drug susceptibility patterns. They were also able to show that the infectivity of treated patients, even those with resistant organisms, yielded lower rates of infectivity. By means of these studies, Riley and colleagues showed that tuberculosis was airborne, that infectivity of different strains differed and that infectivity was reduced with treatment, even in the case of resistant organisms. Sammy Saab, MD Chief Resident Department of Medicine University of California San Diego
100 apples divided by 15 red herrings: a cautionary tale from the mid-19th century on comparing hospital mortality rates lezzoni LI. Ann Intern Med 1996;124:1079-85.
In this historical look at calculation of hospital statistics, Iezzoni cites the example of Florence Nightingale's use of hospital mortality rates to make a case for the dangers of the London hospitals of the 1860s. Fresh from the Crimean War and having made m o n u m e n t a l changes in military hospital care, Nightingale set about changing civilian institutions. Along with William Farr, a physician and social reformer who had done social statistic analyses for the government, Nightingale calculated the mortality rates for those using London hospitals and those in less urban areas of Britain. The method used by Farr and Nightingale to determine the rates revealed a 90.84% mortality rate for the London hospitals, compared with about 40% in provincial hospitals and 16% in military hospitals. These rates were calculated by taking the n u m b e r of patients dying in hospital in all of 1861 and dividing by the number of patients in hospital on a single day (April, 8 1861). What seems like an absurd calculation was put to good use in pushing for changes in what were seen as very dangerous hospitals of the age. By using these spurious statistics, Nightingale achieved her goals. This is an interesting historical perspective on something we read every day: rates in medical literature. Iezzoni presents an argument through example for using care when interpreting results, particularly when the method of analysis for a given rate is poorly presented or not explained at all. In the introduction, she points to the many quality measures being presented in today's literature and by the news media, often by those who would have us believe that an increase in quality
Leland S. Rickman, MD Marguerite McMillan Jackson, RN, PhD University of California San Diego Medical Center
The cholera near Golden Square Snow d. Excerpted from: Snow d. Snow on cholera. Cambridge (MA): Harvard University Press, 1949.
This classic descriptive epidemiologic study provides an important example for current studies. In it, Snow describes his experience during a 1-month p e r i o d with a cholera epidemic in London. The goal of the study was to determine the source of the outbreak and prevent further spread of the disease. He took a methodical approach to the investigation, beginning by determining when the outbreak began by obtaining a list of deaths from cholera in a 1-week period. After determining the exact day of the outbreak, he then plotted the location of each death on a m a p to determine where the disease began and h o w far it had spread. After noticing a cluster of infections around the Broad Street pump, he interviewed several persons who lived in the area to determine the attack rate among those who drank from the well. The outbreak was determined to be point-source in nature, and Snow r e c o m m e n d e d the removal of the p u m p to limit the spread of cholera. After the removal of the p u m p handle, the incidence of cases dropped dramatically. Several epidemiologic tools were used beneficially in this study. Examples include the epidemiologic curve, the spot map, and the attack rate. These techniques are still used by infection conAJIC Am J Infect Control 1997;25:65-9. Copyright © 1997 by the Association for Professionals in Infection Control and Epiderniology, Inc. 0196-6553/97
$5.00 + 0
17/51/78612
trol professionals to specify the time, place, and persons involved in an outbreak. Snow's methods were enhanced by his thorough investigation. By examining all aspects of the outbreak, he was able to determine the source of the outbreak, as well as the mode of transmission. The only limitation to this study is the fact that most of the residents fled the area when the outbreak reached its peak. Whether removal of the p u m p handle in itself significantly decreased the attack rate will never be known. Although Snow's investigation occurred more than a century ago, his study remains the basis for m o d e m outbreak investigations, from small clinics to the largest metropolitan hospitals. A n d r e w C. Zau
MPH Student Graduate School of Public Health San Diego State University
A e r i a l d i s s e m i n a t i o n of p u l m o n a r y t u b e r c u l o s i s : a t w o - y e a r s t u d y of c o n t a g i o n in a t u b e r c u l o s i s w a r d Riley RL, Mills CC, Nyka W, Weinstock N, Storey PB, Sultan LU, et al. Am J Hyg 1959;70:185-96.
I n f e c t i o u s n e s s of a i r f r o m a t u b e r c u l o s i s w a r d : u l t r a v i o l e t i r r a d i a t i o n of i n f e c t e d air: c o m p a r a t i v e i n f e c t i o u s n e s s of different patients Riley RL, Mills CC, O'Grady F, Sultan LU, Wittstadt F, Shivpuri DN. Am Rev Respir Dis 1962;85:511-25.
We take for granted h o w the infectivity of certain diseases have been elucidated. When people sneezed in the Middle Ages, the words "God bless you" were not to express sympathy for one's immediate health, but to offer hope against losing one's soul. Although it was generally believed that 65
AJIC 66
Reviews
tuberculosis was spread by the air passages (Keers RY, Rigden BG, Yound FH. Pulmonary tuberculosis. Livingstone: Edinburgh, 1945:43-54), it was not until Riley and coworkers published these two landmark studies that the aerosol infectivity of Mycobacterium tuberculosis was firmly established. In one study, the investigators constructed an air-ventilation system in which air flowed from the ward rooms of patients with active pulmonary tuberculosis to a separate, distant r o o m containing guinea pigs. The guinea pigs, housed in cages, were arranged in a grid. All cages received equal air flow. To prevent other sources of tuberculosis infection, including cross-infection among the guinea pigs, the cage floors were made of wire mesh and contained no bedding material. The guinea pigs underwent monthly tuberculin skin tests. Maintenance personnel were also periodically screened with skin tests. Of 373 guinea pigs that were housed in the cages during a 2-year period, 77 were found to react to the tuberculin skin test, and tuberculous infection was found in 71 after they were killed. Primary pulmonary tuberculosis was found in 51 of the 71 guinea pigs. Guinea pigs were not believed to infect each other, because the distribution of infections did not differ significantly from chance and the guinea pigs that had tuberculin reactions were removed before they were believed to be infectious. The drug-sensitivity spectra of M. tuberculosis were almost identical between isolates from the sputum of patients with tuberculosis and isolates obtained from the autopsies of guinea pigs who reacted to the tuberculin skin tests when the respective patients were present. In another study, these investigators provided further evidence that tuberculosis was transmitted by air by showing that infectivity was eliminated with UV irradiation. UV irradiation had previously b e e n s h o w n to sterilize aerosol microbes (Riley RL, Wells WF, Mills CC, Nyka W, McLean RL. Air hygiene in tuberculosis: quantitative studies of infectivity and control in a pilot ward. Am Rev Tuberc 1957;75:420-31.). Air flow was directed from the wards of patients with pulmonary tuberculosis to two separate rooms by w a y of air ducts. The rooms contained cages that housed guinea pigs. Air flow to one of the guinea pig rooms underwent UV irradiation; the other r o o m received untreated air. Only guinea pigs w h o received u n t r e a t e d air acquired tuberculosis. Guinea pigs that breathed irradiated air did not acquire tuberculosis. Again, the experimenters
February 1997
were able to determine which patients were most infectious on the basis of drug susceptibility patterns. They were also able to show that the infectivity of treated patients, even those with resistant organisms, yielded lower rates of infectivity. By means of these studies, Riley and colleagues showed that tuberculosis was airborne, that infectivity of different strains differed and that infectivity was reduced with treatment, even in the case of resistant organisms. Sammy Saab, MD Chief Resident Department of Medicine University of California San Diego
100 apples divided by 15 red herrings: a cautionary tale from the mid-19th century on comparing hospital mortality rates lezzoni LI. Ann Intern Med 1996;124:1079-85.
In this historical look at calculation of hospital statistics, Iezzoni cites the example of Florence Nightingale's use of hospital mortality rates to make a case for the dangers of the London hospitals of the 1860s. Fresh from the Crimean War and having made m o n u m e n t a l changes in military hospital care, Nightingale set about changing civilian institutions. Along with William Farr, a physician and social reformer who had done social statistic analyses for the government, Nightingale calculated the mortality rates for those using London hospitals and those in less urban areas of Britain. The method used by Farr and Nightingale to determine the rates revealed a 90.84% mortality rate for the London hospitals, compared with about 40% in provincial hospitals and 16% in military hospitals. These rates were calculated by taking the n u m b e r of patients dying in hospital in all of 1861 and dividing by the number of patients in hospital on a single day (April, 8 1861). What seems like an absurd calculation was put to good use in pushing for changes in what were seen as very dangerous hospitals of the age. By using these spurious statistics, Nightingale achieved her goals. This is an interesting historical perspective on something we read every day: rates in medical literature. Iezzoni presents an argument through example for using care when interpreting results, particularly when the method of analysis for a given rate is poorly presented or not explained at all. In the introduction, she points to the many quality measures being presented in today's literature and by the news media, often by those who would have us believe that an increase in quality