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Resurgent and emergent disease in a changing world Mitchell L Cohen Division of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA Emerging infectious diseases pose important public health problems for both the developed and developing world. Many new or previously unrecognized bacterial, fungal, viral, and parasitic diseases have emerged within the past two decades. At the same time, many once-controlled infections have re-emerged or become resistant to antimicrobial therapy. This emergence is the result of changes in society, technology, the environment, and the microbes themselves, and these changes have had often unpredictable consequences. Important factors influencing emergence include changes in human demographics and behaviour, changes in technology and industry, changes in economic development and land use, increasing and rapid international travel and commerce, microbial adaptation and change, and the breakdown of public health measures. Addressing emerging infectious diseases will require international and interdisciplinary partnerships to build an appropriate infrastructure to detect and respond to these often unanticipated threats to health. Correspondence to Mitchell L Cohen, Division of Bacterial and Mycotic Diseases (C09), National Center for Infectious Diseases, Centers for Disease Control and Prevention (CDC), 1600 Clifton Road, Atlanta, GA 30333, USA For most of the last millennium, life was short and often unexpectedly ended by an infectious disease. Median life expectancies ranged from 20—40 years, and although the impact of infectious diseases was greatest among the poor, all classes of society were affected. Endemic infections led to high infant mortality, and populations remained relatively stable only by high birth rates offsetting the high death rates. Epidemic diseases, such as plague and cholera, would devastate entire communities. In many military campaigns, deaths from infections in camp would exceed the mortality in battle. Infectious diseases were a major influence in all aspects of life. Beginning in the 17th century, a series of changes rapidly influenced the frequency of infectious diseases. Improved agriculture led to better nutrition, enabling persons to resist infection or survive illness better. In the 19th century, improved hygiene and sanitation and safer food and water reduced the transmission of many infectious diseases. Knowledge of the specific etiology of infectious diseases for the first time provided British Mtdical Bulletin 1998,54 (No 3) 523-532 CThe British Council 1998 Resurgent/emergent infectious diseases a scientific basis for prevention strategies and treatment. In the 20th century, continued environmental improvement and scientific advances, specifically the advent of immunization and antibiotics, provided additional ways to prevent transmission as well as treat the individual patient. So extensive was the impact of these factors that in less than 100 years, the three leading causes of death in the US changed from tuberculosis, pneumonia, and diarrhoea to heart disease, cancer, and stroke. Between 1900 and 1985, the rate of natural causes of death for children aged 1—4 years old in the US fell from 18.4 per thousand to 0.2 per thousand1. The median life span increased from 47 years to almost 76 years. Much of this change resulted from the prevention and treatment of infectious diseases. Despite these improvements, there were indications for concern. Worldwide, infectious and parasitic diseases remained the leading cause of death, accounting for almost 20 million deaths in 19922. Even in the developed world, there were troubling trends. In the last two decades, death rates from respiratory infections and septicemia have increased, and organisms such as human immunodeficiency virus (HTV) have emerged to become leading causes of morbidity and mortality. Between 1980 and 1992, the mortality rate from infectious diseases in the US rose 58%, from 41 to 65 per 100 000 population3. These trends did not go unnoticed. In October 1992, the Institute of Medicine (IOM) published a report titled, Emerging infections: microbial threats to health in the United States4. In this report, the IOM defined an emerging infection as 'a new, emerging, or drug-resistant infection whose incidence in humans has increased within the past two decades, or whose incidence threatens to increase in the near future'. Thus, emerging infectious diseases represent not only the previously unrecognized bacteria or viruses - Legionella or Ebola - but also the wellrecognized diseases - cholera, coccidioidomycosis, malaria, or dengue that have re-emerged as important public health problems. In this article, I examine some of the recent trends in emerging infectious diseases, particularly focusing on bacterial and fungal diseases, and the factors influencing their emergence. Trends in emerging infectious diseases The last two decades have seen a series of newly recognized diseases. These include bacterial diseases, such as Legionnaires' disease, toxic shock syndrome, Lyme disease, campylobactenosis, food- and waterborne infections caused by Escherichta coli O157:H7, Vibrio vulnificus and Vibrio cholerae O139, Helicobacter infections, ehrlichiosis, and 524 British Medical Bulletin 1998,54 (No 3) New and emerging infectious diseases Bartonella infections; viral diseases, caused by Marburg virus, Ebola virus, hantavirus, and HIV; parasitic diseases, such as cryptosporidiosis and cyclospora infections; fungal diseases, including a variety of molds and yeasts; and spongiform encephalopathies, such as bovine spongiform encephalopathy, which are not easily categorized. At the same time, a number of known diseases have re-emerged as important public health problems. An examination of the bacterial diseases alone defines the magnitude of this problem. In 1991, cholera became epidemic in the Western hemisphere for the first time in over 100 years, rapidly spreading to involve almost every nation and causing over one million cases and 11 000 deaths5. In the early 1990s, diphtheria became epidemic in many of the nations of the former Soviet Union. The group A Streptococcus caused clusters of invasive disease in Europe and the US, capturing the media's attention as the 'flesh-eating' bacterium. Listerta was first recognized as a foodborne pathogen in the early 1980s and was subsequently implicated in epidemics especially affecting pregnant women and compromised hosts. Serogroup A Neisseria meningitidis remains epidemic in many parts of the world; in 1996, it caused over 150 000 thousand cases and 16 000 deaths in sub-Saharan Africa alone6. Strains of serogroups B and C N. meningitidis are causing clusters of illness in cities and on college campuses in countries of the developed world. Salmonella ententidis, which is primarily associated with contaminated shell eggs, has become the most common Salmonella serotype. In parts of Africa and Asia, multidrug-resistant Shigella dysenteriae infections are causing epidemics with greater than 10% mortality rates and hundreds of thousands of fatalities7. Tuberculosis, a persistent problem of the developing world, accounting for almost 3 million deaths each year, has resurged in many parts of the developed world, often in a drug-resistant form. Two areas in the IOM's report on emerging infections received particular emphasis - foodborne disease and antimicrobial resistance. The report highlighted the potential of foods to be involved in the emergence of infectious diseases 'because there were many points at which food safety could be compromised'. Well-recognized diseases such as salmonellosis, cholera, and listeriosis have become increasingly important public health problems. At the same time, new diseases such as campylobacteriosis, and new organisms such as E. coli O157:H7, and V. cholerae 0139 have emerged. In the US, the frequency of salmonellosis has doubled since 1970. Campylobacter was not recognized until the late 1970s but is now known to be the most common bacterial cause of diarrhoeal disease in the US. E. coli O157:H7, first recognized m 1982, now accounts for an estimated 20 000 cases and 250 deaths each year in the US. alone8. The IOM also identified antimicrobial resistance as an important contributor to the emergence of infectious diseases. In the hospital, British Medical Bulletin 1998,54 (No 3) 525 Resurgent/emergent infectious diseases certain strains of enterococci and Mycobacterium tuberculosis are essentially untreatable with antimicrobial drugs. Infections with multiple drug-resistant Gram-negative rods are endemic in many hospitals, the specific predominant species varying from hospital to hospital. The greatest public health risk, however, is the increasing frequency of methicillin-resistant Staphylococcus aureus (MRSA). Of S. aureus infections in US hospitals, 20—40% are caused by MRSA9. Many of these strains are multidrug resistant or susceptible only to vancomycin. Since recent reports from Japan and the US describe S. aureus with decreased susceptibility to vancomycin, it is only a matter of time before untreatable staphylococcal infections will be occurring10. Antimicrobial resistance was once perceived as primarily a problem in hospital-acquired infections. In recent years, however, communityacquired bacteria have become increasingly drug resistant, posing important diagnostic and public health dilemmas. Increasing resistance is being seen in the gonococcus, Haemophilus influenzae, Shigella, Salmonella, and the pneumococcus. In the developing world, strains of Shigella dysenteriae and Salmonella typhi are susceptible only to the newer fluoroquinolones and extended-spectrum cephalosporins. In the developed world, multiresistant strains of non-typhoid Salmonella are increasing, and in some areas, such as the UK, strains are becoming resistant to the newer fluoroquinolones11. Perhaps of greatest concern in community-acquired infections is the increasing resistance among pneumococci. In some areas of the US, over 20% of pneumococcal isolates express high-level resistance to penicillin and 10% are resistant to extended spectrum cephalosporins12. Some physicians are already adding vancomycin to the empirical treatment for meningitis. Since pneumococcal disease accounts for over 2 million cases of pneumonia, 7.5 million cases of otitis media, and 3000 cases of meningitis each year in the US alone, the emergence of resistance is a grave public health concern. Factors influencing emergence The emergence of infectious diseases is primarily related to change. As the 19th century orator, Robert G. Ingersoll, pointed out, in nature there are neither rewards nor punishments, only consequences. Thus, when there are changes in society or technology, there are consequences. Some of these consequences may be small; others may be monumental. Many of the consequences are unexpected. The various changes influencing emergence affect six factors that were identified by the IOM4. These are human demographics and behaviour, technology and industry, economic 526 British Medical Bulletin 1998,54 (No 3) New and emerging infectious diseases development and land use, international travel and commerce, microbial adaptation and change, and the breakdown of public health measures. It is helpful to examine the nature of the changes in these areas and the impact they have on infectious diseases. Human demographics and behaviour Important factors in changing human demographics include increases in the number of susceptible persons, the use of day care, and immigration. A series of factors are causing a rise in the number of susceptible persons and the greater the percentage of the population that is susceptible to infectious diseases, the greater the potential for disease transmission. In many countries in the developed world, the number of older individuals is growing. Since aging is associated with an increased susceptibility to infectious diseases, the potential for disease transmission is also increasing in these countries. In the US, the percentage of the population over 65 years was about 4% in 1900 and will reach almost 25% in 204013. Certain underlying diseases are also placing more patients at risk for various infectious diseases, and these have also increased. For example, the reported incidence of diabetes mellitus in the US increased from 0.5% of the nation's population in 1935 to over 3% in 199514. It is estimated that there are actually 16 million persons with diabetes in the US, so the true incidence of this disease may be greater than 5% of the population. The rates for many malignancies are also increasing, and these patients have increased susceptibility to infectious diseases from the disease process, during chemotherapy and, in some cases, lifelong even after cure15. Some of the most highly susceptible patients are those receiving immunosuppressive therapy following organ transplantation. Almost 20 000 organ transplants were performed in the US in 199516. Worldwide, the greatest factor increasing susceptibility may be the spread of HTV, which has led to millions of persons at increased risk for a variety of infectious diseases Societal changes, like the increased use of day care, are also affecting the emergence of infectious diseases. The increasing frequency of both parents working outside the home, or of single parent families, has led to greater use of day care. The combination of susceptible children, inadequate hygiene, frequent infections, and frequent antimicrobial use is the perfect setting for the emergence of antimicrobial resistance. Thus, it is no surprise that day care attendance has been an important factor associated with the emergence of penicillin-resistant Streptococcus pneumoniae. A recent Kentucky study demonstrated a 4-fold greater relative risk for colonization with a high-level penicillin-resistant Streptococcus pneumoniae among children attending day care17. British Medical Bulletin 1998,54 (No 3) 527 Resurgent/emergent infectious diseases The increase in immigration and changing patterns of immigration are also contributing to the emergence of infectious diseases. Between 1984 and 1992, 0.5-1.5 million immigrants and refugees were admitted to the US each year18. In contrast to the previous waves of immigration, many of these individuals came from parts of the world where certain infections, such as tuberculosis, are common. This is an important factor in the resurgence of tuberculosis in the US, as the percentage of patients who were foreign-born increased from 22% in 1986 to 37% in 199619. A variety of human behaviours are also influencing the emergence of infectious diseases. The impact of the sexual revolution on the frequency of gonorrhoea, syphilis, and HIV is evident. Perhaps less evident is the impact of other changes, such as changes in eating habits. There are changes in the types of food that people are eating, how those foods are prepared, and where the foods are prepared. This can lead to new exposures to unfamiliar foods or the dependency upon others to handle and prepare food safely. All these factors have contributed to the emergence of some of the newer foodborne diseases8. Another important behaviour influencing the emergence of resistance has been the unnecessary use of antimicrobial agents. In 1992, over 110 million courses of antimicrobial drugs were prescribed to outpatients in the US20. Since three-quarters of these drugs are prescribed for upper respiratory infections that are often caused by viruses, over half of these 110 million courses may be unnecessary. Technology and industry The impact of technology and industry falls into three general areas. These include new technologies and products, changes in food production processing and preservation, and changes in industrial demographics. New technologies and products may have unexpected disease implications, such as the association of air conditioning and whirlpool spas with Legionnaires' disease, or new tampons with toxic shock syndrome, or the fast-food hamburger with E. colt O157:H7. The second area, changes in how food is produced, processed, and preserved, has also been important. For example, in the last 50 years many of the new agricultural production strategies involve intensive rearing of young animals under environmental conditions that are conducive to the transmission of infectious diseases. These production strategies often depend upon increased antimicrobial use. Thus, only substituting young animals for children, the situation is similar to the day care setting and has resulted in an increase in antimicrobial resistance for organisms that are transmitted through the food chain from animals to humans. Between 1979 and 1989, the frequency of drug 528 British Medical Bulletin 1998,54 (No 3) New and emerging infectious diseases resistance in human Salmonella isolates almost doubled from 17% to 31% 21 . Today the resistance in humans is the result of antimicrobial use in animals. The many changes in food processmg and preservation are also influencing disease emergence. The recent emphasis on 'natural' foods has led to use of fewer preservatives or secondary barriers to prevent spoilage. Thus, some foods are protected only by refrigeration. This has resulted in increasing problems with organisms that grow in the cold, such as Listeria or Yersinia. The lack of secondary barriers also increases the risk of food handling errors leading to diseases such as botulism. In the last 10 years, several outbreaks of botulism have occurred when 'keep refrigerated' foods were not kept refrigerated. The third change, that of industrial demographics, is characterized by consolidations of industry, larger market size, and wider geographic distribution for a variety of food products. Although these changes have the potential for greater quality control and better safety, when something goes wrong, it can really go wrong. Thus, in 1994, an ice cream product produced by a single company in Minnesota led to thousands of cases of salmonellosis in over 41 states22. Economic development and land use Changes in economic development and land use are often cited in discussions of emerging viral diseases. Encroachment on rain forests, for instance, may lead to exposure to new agents such as Ebola or Marburg viruses. However, such changes are also influencing the emergence of other infectious diseases. For example, population growth and spread lead to environmental change and pollution. The inadequacies of hygiene and sanitation that exist in many of the 'mega cities' in the developing world are potential ticking time bombs for the emergence of infectious diseases23. Other types of development and land use practices are contributing to specific problems. Conservation activities, such as those directed toward deer populations, have contributed to the emergence of Lyme disease. Coastal agriculture expansion is leading to blooms of toxic microorganisms, while coastal population growth is leading to human faecal contamination of shellfish beds and transmission of a variety of viral and bacterial pathogens. The variation in environmental conditions, whether natural or man-made, can lead to the emergence of infectious diseases. In 1992-1993, the rainfall in the southwestern US was well above normal; this led to increased vegetation, and consequentially, to larger rodent populations. The increase in rodent populations resulted in greater contact with humans and the eventual outbreak of the first recognized epidemic of hantavirus infections in the US24. British Medical Bulletin 1998,54 (No 3) 529 Resurgent/emergent infectious diseases International travel and commerce Advances in technology have had a rapid impact on international travel and commerce. A person or a food can be almost anywhere in the world in 24—48 hours. This facility in travel and commerce has increased the potential for the introduction of emerging pathogens to new geographic areas by infected travellers, by contaminated food, or even by transporting vehicles. The latter case is demonstrated by the introduction of the epidemic strain of V. cholerae from Central and South America into the oyster beds of Mobile Bay in the US. This introduction was attributed to the discharge of contaminated bilge water by ships entering Mobile Bay25. Microbial adaptation and change As human-kind is instituting a number of changes, the microbes themselves are changing. This is leading to the evolution of new pathogens, the development of new virulence factors, the development of antimicrobial resistance, and tolerance to adverse environmental conditions. A good example of this microbial change has been the emergence of E. coli O157:H7, which probably evolved from an enteropathogenic E. colt that acquired Shigella genes26. As a foodborne pathogen, it combines the worst of Shigella and Salmonella. Like Shigella, this organism has a low infectious dose, requiring only a few organisms to cause disease. This leads to subsequent person-to-person transmission once the organism is introduced into a community and also poses a high risk for cross-contamination in the kitchen. This organism is more similar to Salmonella in its tolerance to adverse environmental conditions. Thus, it has been associated with outbreaks that were caused by foods with pH 4.0, conditions that are usually inhibitory to most bacterial pathogens. The breakdown of public health measures The breakdown of public health measures has been the result of a series of often unrelated factors. Earlier successes in the war against infectious diseases led to complacency. This, coupled with limited resources and competing priorities in public health, often led to the transfer of resources from infectious diseases to other areas or to newly emerging infections. Thus, the emphasis on noninfectious diseases and the emergence of HTV has led, in some health departments, to resources being shifted away from diseases such as tuberculosis. When 530 British Medical Bulletin 1998,54 (No 3) New and emerging infectious diseases tuberculosis re-emerged, it was frequently caused by drug-resistant organisms, since much of the curtailed public health activities had been directed toward assuring infected individuals received complete courses of appropriate antituberculosis drugs27. In many parts of the world, sanitation and hygiene are inadequate, and even in parts of the developed world, the systems are aging or inadequately designed, increasing vulnerability to outbreaks such as that which occurred in Milwaukee with over 400 000 cases of cryptosporidiosis28. The impact of the breakdown of public health measures can easily be seen during wars, population movements, and natural disasters. One such example has been the emergence of epidemic dysentery in Africa. Since 1979, massive epidemics of dysentery caused by Shigella dysentenae type 1 have occurred in cities, rural areas, and refugee camps in Central and Southern Africa. The epidemics have affected all age groups, often with case-fatality ratios greater than 10%. In 1991 alone, the disease caused 60 000 deaths in Burundi and at least 200 000 deaths in the rest of Africa7. In contrast to Shigella species, which are more common in parts of the developed world, this organism is essentially resistant to all available oral antimicrobial drugs. Some of the newer fluoroquinolones are the last remaining effective oral agents. Conclusion Infectious diseases have played an important role in the history of humanland and will likely be important in its future. Although great progress has been made against infectious diseases, humans are vulnerable to the emergence of new diseases or re-emergence of well-recognized infectious diseases. The changes in society and technology, often occurring at an escalating rate, are contributing both to the likelihood of and vulnerability to this emergence. The impact of these changes and the resultant emergence are often unpredictable. Thus, addressing emerging infectious diseases requires a strong public health infrastructure to detect and rapidly respond to these emerging threats to health. References National Center for Health Statistics. L. Fingerhut. Trends and current status in childhood mortality, United States, 1900-85. Vital and Health Statistics, Series 3, No. 26. Washington, DC: US Government Printing Office, 1989 World Health Organization. Global health situations and projections, estimates, 1992. Geneva: WHO, 1992 Pinner RW, Teutsch SM, Simonsen L et al. Trends in infectious diseases mortality in the United States. JAMA 1996; 275. 189-93 British Medical Bulletin 1998,54 (No 3) 531 Resurgent/emergent infectious diseases 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 532 Institute of Medicine. Emerging infections: microbial threats to health in the United States Washington, DC: National Academy Press, 1992 Pan American Health Organization Cholera situation in the Americas, Update No. 14. Washington, DC: Pan American Health Organization, 1996 World Health Organization. Meningococcal meningitis — update. Geneva: WHO, 1997 Ries AA, Wells JG, Olivola D et al. Epidemic Shtgella dysentenae Type 1 in Burundi: panresistance, and implications for prevention. / Infect Dis 1994; 169: 1035—41 Altekruse SF, Cohen ML, Swerdlow DL. Emerging foodborne diseases. Emerg Infect Dis 1997; 3: 285-93 Cohen ML. Antimicrobial resistance: prognosis for public health. Trends Mtcrobiol 1994, 2: 422-5 Centers for Disease Control and Prevention. Update; Staphylococcus aureus with reduced susceptibility to vancomyan - United States, 1997. MMVCR Morb Mortal Wkly Rep 1997; 46: 813-5 Threlfall EJ, Frost JA, Ward LR et al. Increasing spectrum of resistance in multiresistant Salmonella typhimunum. Lancet 1996; 347- 1053^ Cetron MS, Breiman RF, Jorgensen JH et al. Multisite population-based surveillance for drugresistant Streptococcus pneumomae (Abstract C-283) 91th General Meeting American Society for Microbiology. Washington, DC' American Society for Microbiology, 1997 US Department of Commerce, Bureau of the Census. 1990 Census of population. General population characteristics. Washington, DC: US Government Printing Office, 1990 Centers for Disease Control and Prevention. National prevalence of diabetes in the US. Diabetes Fart Sheet, 1995 American Cancer Society. Cancer facts and figures — 1996 Atlanta: American Cancer Society, 1996 Dixon DM, McNeil MM, Cohen ML et al. Fungal infections: a growing threat. Public Health Rep 1996; 111: 226-35 Duchrn JS, Breiman RF, Diamond A et al. High prevalence of multidrug-resistant Streptococcus pneumoniae among children in a rural Kentucky community. Pediatr Infect Dis J 1995; 14: 745-50 US Immigration and Naturalization Service. Statistical yearbook of the immigration and naturalization service. Washington, DC US Government Printing Office, 1991 Centers for Disease Control and Prevention. Tuberculosis morbidity - United States, 1996. MMWR Morb Mortal Wkly Rep 1997; 46 695-700 McCraig LF, Hughes JM. Trends in antimicrobial drug prescribing among office-based physicians in the United States JAMA 1995; 273 214-9 Lee LA, Puhr ND, Maloney EK et al. Increase in antimicrobial-resistant Salmonella infections in the United States, 1989-1990 / Infect Dis 1994; 170: 18-34 Hennessey 1 W, Hedberg CW, Slutsker L et al. A national outbreak of Salmonella enteritidts infections from ice cream. N Engl ] Med 1996; 334: 1281-6 Garrett L. The coming plague: newly emerging diseases in a world out of balance. New York: Farrar, Straus, and Giroux, 1993 Hughes JM, Peters CJ, Cohen ML et al Hantavirus pulmonary syndrome: an emerging infectious disease. Science 1993; 262: 850-1 Centers for Disease Control. Isolation of Vibrio cholerae Ol from oysters - Mobile Bay, 1991-1992. MMWR Morb Mortal Wkly Rep 1993; 42: 91-93 Whittam TS, Wolfe ML, Wachsmuth IK et al. Clonal relationships among Escherichia coll strains that cause hemorrhagic colitis and infantile diarrhea. Infect Immun 1993; 61' 1619-29 Bloom BR, Murray CJL Tuberculosis, commentary on a reemergent killer. Science 1992, 257: 1055-64 MacKenzie WR, Hoxic NJ, Procter ME et al A massive outbreak in Milwaukee of Cryptospondium infections transmitted through the public water supply. N Engl J Med 1994; 331: 161-7 British Medical Bulletin 1998,54 (No 3)