In medical school curricula, and in continuing education programs for graduate physicians, it is quite rare for human health afflictions to be presented in the context of society at large. Discussions of illness almost never consider the ways in which societal and natural changes can impact patterns of disease, and yet these impacts and resultant changes can be quite profound.
Among the most striking examples of the ways in which changes in society and the environment can influence disease patterns are those found in my own discipline of infectious diseases.
TYPES OF CHANGING PATTERNS OF INFECTIOUS DISEASES
A dramatic type of change is the recognition of a new disease; acquired immune deficiency syndrome (AIDS) and severe acute respiratory syndrome (SARS) are obvious examples. Other so-called new diseases represent the discovery of a microorganism which has been with us and producing illness for a long time but whose role as a pathogen was unappreciated because of inadequate laboratory diagnostic techniques; the bacterial diarrheal pathogens Campylobacter and Escherichia coli O157:H7 serve as examples.
Another change is new geographic ranges for old diseases. International air travel has made it possible for someone incubating an exotic illness to present with symptoms upon returning home to her/his native country where the disease is not normally present; malaria and typhoid fever presenting upon return to the United States after travel abroad are good examples.
We have new populations at risk. Children in day care, the elderly in nursing homes, and immunosuppressed transplant recipients are increasing in number, and all represent new populations at risk for infectious diseases.
Some long-recognized and well-known pathogens have acquired new tricks. Streptococcal toxic shock syndrome, a new syndrome produced by the bacterium responsible for most bacterial sore throats and cellulitis, is 1 example. We have also seen new faces for old infections; infant botulism, distinct from traditional food-borne botulism, is 1 such case.
New modes of transmission include human-to-human organ transplantation. More than 1 illness has been transmitted by corneal transplantation, including the ancient scourge rabies. New niches for old pathogens have been created. Osteomyelitis of the small bones of the feet in children who sustain a puncture wound to the foot is most often caused by the water-loving bacterium Pseudomonas aeruginosa. The reservoir for the pseudomonads, which thrive where it is warm, moist, and dark, is the inner layers of the sneakers worn almost constantly by all American children.1 When children wore leather-sole shoes and only put on sneakers to run or play basketball or tennis, Pseudomonas osteomyelitis was unknown.
CAUSES OF CHANGES
Among the causes of the changing patterns of infectious diseases are alterations in lifestyle, including travel patterns, sexual behavior, dietary trends, pet acquisition, changes in the workforce, use of leisure time, and our culture of youth and beauty. Other important causes include the impacts of alternative medicine, medical progress, international politics, religion, and the weather.
Some illustrative examples of specific changes follow.
Every day, more than 2 million persons get in an airplane in 1 country and land in another. More and more US citizens are traveling to other parts of the world including tropical areas where parasitic illnesses are endemic. Sometimes, travelers bring back souvenirs other than those they intended to bring.
Some years ago, as a member of the Zoological Society of Philadelphia, I received an invitation to travel to Rwanda and see mountain gorillas. I was tempted but decided that the cost of the trip would be put to better use for my college-bound son. A woman who lives within a couple of miles of my home did make the trip. As the tourists entered the van on the way to see the gorillas, they were handed fly swatters and advised by a guide to "kill the tsetse flies before they bite you." Upon her return home, the woman became ill with high fever, severe headache, and muscle aches and sought her physician's help. That evening, an alert laboratory technician reviewing the blood smears done as part of a complete blood cell count saw the telltale parasites and made a diagnosis of African sleeping sickness.2
An unusual example of a work-related illness, and a cautionary tale, can be found in the following: the adult film industry in Los Angeles County, California includes more than 200 production companies which employ more than a thousand film stars who regularly engage in work-related sex. One of these stars, a 40-year-old man, tested negative for the human immunodeficiency virus (HIV) in March of 2004 but was positive when tested a month later. Not long before his last negative test, he had unprotected sex while making a film in South America. When he returned to the United States, and before his positive HIV test, he had unprotected film-related sex with 13 women. Three of these women subsequently developed HIV infection, and the viruses from the male star and the 3 women costars were identical.3
Our television screens are filled with advertisements for remedies to treat erectile dysfunction, and many men seek help from physicians for this problem. Three patients at an impotence clinic developed endocarditis due to an unusual fungus, Phialemonium curvatum.4 Each of these men used a prefilled syringe to self-inject vasoactive drugs into the penis to treat erectile dysfunction. Cultures of unused syringes and bottles grew the same fungus.
Water and Food Safety
Human illness due to ingestion of contaminated water or food is a problem that goes back to antiquity. Now that we get water from large municipal supplies, and food is processed in immense plants with resultant products sent all over the country, there is potential for large and widespread epidemic disease.
In 1993, contamination of the Milwaukee, Wisconsin City water supply resulted in more than 400,000 people developing gastrointestinal illnesses because of the waterborne protozoan parasite Cryptosporidium. The total cost of outbreak-associated illness was calculated to be greater than 96 million US dollars.5
Before 1970, the major cause of mycobacterial lymphadenitis in children was Mycobacterium scrofulaceum; however, since 1975, the major cause has been a different species, Mycobacterium avium.6 What caused the change? The implementation of clean water acts in 1975 increased the chlorination of water. Environmental mycobacteria are less affected by chlorination than other common water organisms, and M. avium is more resistant than other mycobacteria (eg, 5 times more resistant than M. scrofulaceum), hence the change in etiology of childhood cervical and submandibular adenitis.
In 2002, contaminated turkey deli meat led to a multistate epidemic of invasive disease due to the bacterium Listeria monocytogenes.7 Illness occurred in 54 patients in 9 states and resulted in the recall of more than 30 million lb of food products, one of the largest recalls of meat in US history.
Our mothers urged us to eat our vegetables, particularly the green ones. At the time of the writing of this publication in 2006, an ongoing multistate outbreak of E. coli O157:H7 infections had resulted in illness in more than 190 persons in 26 states.8 More than one half were hospitalized, and 16% developed hemolytic uremic syndrome. The vehicle of infection was bagged fresh spinach. What would mother think now?
Contamination of food prepared and distributed by catering services can have a similar impact. A tuna and corn salad, tainted with L. monocytogenes and distributed by a caterer to 2 school cafeterias as part of a school lunch program, resulted in febrile diarrhea in 1566 persons, mostly young children; 192 were hospitalized.9
Dietary trends and food fads can affect patterns of disease. The eating of the aesthetically prepared and served Japanese raw fish delicacies known as sushi has become very popular; most metropolitan areas in the United States have sushi bars.
A physician developed abdominal pain, distention, diarrhea, and weight loss. After some time, he passed a 4-foot-long fish tapeworm of the genus Diphyllobothrium. Before the onset of his illness, he had attended a party at which sushi was served; 3 other physicians who attended the same party and ate the sushi also developed symptomatic tapeworm infection.10 For generations, in this country, fish tapeworm infestation was seen primarily in Jewish housewives who acquired the parasite while preparing gefilte fish and tasting the raw fish for seasoning. With the popularity of sushi and the decline of homemade gefilte fish, the pattern of fish tapeworm infection is changing.
Specialty foods prized by certain ethnic groups have also been associated with epidemic disease. In 2002, an outbreak of listeriosis occurred in North Carolina among Hispanic persons, most of whom were pregnant, a well-known risk factor for listerial infection.11 The affected individuals had consumed illicitly produced Mexican-style cheese they purchased from door-to-door vendors.
Dogs and cats remain the dominant household pets, but more and more Americans are sharing their homes with exotic animals such as iguanas, ferrets, snakes, and African rodents. In 2003, a cluster of monkeypox cases appeared in the US Midwest, the first appearance in the Western hemisphere of this viral zoonotic disease that causes fever and a blister-forming rash.12 Seventy-two people became ill after contact with pet prairie dogs. These native prairie dogs had been housed with rodents imported from Ghana that were thought to be the primary source of the outbreak.
Workforce Changes and New Populations at Risk
The soaring divorce rate in the late 1970s and early 1980s fed the growing day-care industry. More recently, there has been an increase in the number of families in which both parents work, hence the continuing growth of day care. There are now more than 15 million American children in day care. Day-care centers are potentially hotbeds of disease transmission and acquisition, and outbreaks due to a variety of pathogens including viruses, bacteria, and parasites have occurred in the setting of day care. On the other hand, early exposure to certain illnesses during day care may confer a health benefit. It has been shown that children in day care had almost twice as many colds at the age of 2 years as those cared for at home; however, from ages 6 to 11 years, former day-care children had only one-third as many colds as children who stayed home.13 The advantage disappeared by adolescence.
At the other end of the age spectrum is another population at risk, the elderly, who make up the fastest growing segment of our population. Many of these individuals are cared for in nursing homes and assisted-living facilities where outbreaks of influenza, for example, are common.
More and more individuals are receiving transplanted organs; these persons, because of posttransplant immunosuppression, are at risk for opportunistic infections that were once quite rare and are now seen routinely at major medical centers.
Picture this: a group of young adolescent girlfriends gather for a slumber party and spend a couple of hours in a wooden hot tub. They sleep in their bathing suits. Within 2 days, each girl develops an intensely itchy rash that is most prominent in the areas covered by her bathing suit, particularly the buttocks.14 The girls give their affliction the name, "Hot Tub Buns." Pseudomonas folliculitis, the medical name for the girls' problem, was virtually unheard of until the late 1970s when reports of this condition began to appear coincident with an explosive increase in hot tub, saunas, and whirlpools in private homes and health clubs. Other microorganism-related problems associated with hot tub use include Legionnaires disease, free-living ameba infections of the cornea in those who wear contact lenses in the hot tub, and a pneumonitis, also known as "hot tub lung", apparently caused by hypersensitivity to a mycobacterial antigen.15
An 8-year-old girl was hit in the forehead by a lawn dart. A small cut was cleansed and sutured. Two days later, the girl was quite ill, and pus was coming from the wound. A head scan showed gas in the frontal lobe of her brain. She was taken to the operating room for drainage of an abscess, and culture of a surgical specimen grew Clostridium tertium, a soil organism and a very rare cause of brain abscess.16 There was one time when clostridial brain abscesses were seen with some frequency, and that was during the First World War in those who had bayonet injuries of the head. This little girl acquired the equivalent of a bayonet injury in her own backyard.
Twenty-six persons sought help in an Australian emergency department for infected scratches and pustules covering their bodies.17 The responsible organism was Aeromonas hydrophila, a bacterium associated with water. All the victims had played "mud football" before the infections appeared. The playing field was deliberately created for this annual event when a paddock was irrigated with water pumped from an adjacent river for a month before the game.
Culture of Youth and Beauty
Our national obsession with looking good and youthful has brought some fascinating by-products. To mention just a few examples, there have been outbreaks of mycobacterial infections after breast enhancement surgery, illicit cosmetic injections, and foot baths in nail salons. Artificial fingernails, and the bacteria that like to stick to them, have led to transmission of antibiotic-resistant infections in hospitals without causing any problems for the nail wearer.
More than one third of Americans who routinely receive care from licensed medical physicians are also engaged in some alternative or complementary form of health care.18 Without exception, every AIDS patient in my own practice, when asked, readily came forth with information about unconventional medical practices in which they were engaged, ranging from megavitamin therapy to the weekly administration of rectal ozone. Sometimes, the alternatives bring health hazards of their own.
A 30-year-old man with AIDS and fever was admitted to a Texas hospital. He was found to have septicemia due to Salmonella arizonae. He regularly took capsules containing rattlesnake meat powder; cultures of the capsules grew the same bacterium.19
Shortly after the spirochetal etiology of Lyme disease was defined, a letter from a prominent physician published in a major medical journal20 raised the question of the potential use of malariotherapy for Lyme disease, drawing from the experience of intentionally giving malaria infection to treat neurosyphilis, another spirochetal disease, work for which Wagner-Jaurreg won the Nobel Prize for medicine (more recent analyses show the treatment did not work). Just a few months later, 2 cases of malaria were reported in New Jersey residents who had traveled to a Mexican clinic to receive intramuscular injections of malaria parasites to treat what they believed was Lyme disease.21 Unfortunately, this form of treatment does not cure or improve syphilis or Lyme disease.
Twelve women developed tetanus 1 to 2 weeks after receiving intramuscular injections of fetal sheep cells as alternative treatment for rheumatism; 7 died.22 None had been previously immunized against tetanus.
A 7-day-old baby developed Legionnaires disease.23 The baby had been delivered underwater in a hospital setting. The same Legionella pneumophila type was isolated from the child, the hospital water, and the water from the birthing pool.
Medical progress has brought enormous benefits. Smallpox has been eradicated. Widespread early childhood use of Haemophilus vaccine has made meningitis due to this previously formidable pathogen a rare occurrence. In some parts of the world, hepatitis B vaccine has decreased the frequency of liver cancer.
Medical progress has also brought with it some unexpected surprises. The most common cause of infection complicating foreign body implants such as artificial joints, artificial heart valves, ocular lens implants, and others is Staphylococcus epidermidis, an organism that I was told in medical school is a harmless saprophyte, of consequence only as a laboratory contaminant.
Another surprising and intriguing impact of medical progress may occur as a by-product of the hepatitis B vaccine. In many parts of the world, male children are prized over female children. Changes in sex ratio can have an impact on the sociology and economy of a society. A not-well-known fact is that hepatitis B-infected mothers are more likely to give birth to boys than girls.24 Widespread use of hepatitis B vaccine has already been shown to produce a redistribution of sex percentages with fewer male births.
The past few years have seen reports of human-to-human transmission by organ transplantation of infection due to West Nile virus, lymphocytic choriomeningitis virus, and rabies.
China has the second highest rate of human rabies in the world. In the last decade, the occurrence of this ancient scourge has increased dramatically. From 2001 to 2004, rabies death rates increased by 91%, 36%, 71%, and 34%, respectively, over the previous year.25 In 2003 alone, rabies was responsible for more deaths than AIDS and SARS. Virtually all cases of human rabies were transmitted by dog bites. The recent reversal of a restrictive governmental policy in China is at least partially responsible for the exponential jump in rabies cases. During the long reign of Mao Zedong, pet dogs were scarce in China because they were considered symbols of bourgeois decadence. Mao is gone, and pet dogs are back and with them "mad dog disease."
Wars, with their resultant disruption of societies, have always been accompanied by epidemics in both combatants and civilians. Military personnel engaged in the recent wars in Afghanistan and Iraq have had to deal with infections and the hazards of combat. Three quarters of personnel have had diarrhea, more than two thirds have had respiratory tract infections, and many have had wounds complicated by infection with a highly antibiotic-resistant organism.26
Regrettably, in our unsettled world, the specter of the use of biological agents as instruments of war or terror threatens to change patterns of infections in horrific ways.
Charitable acts and religious practice can affect human health. Thirty-five church members from Pennsylvania traveled to Mexico for a week to work on construction of a church. Within 2 weeks of returning to their homes in the United States, 27 became ill with fever and influenzalike symptoms. They were eventually diagnosed with coccidioidomycosis,27 a fungal infection endemic to parts of Mexico and the southwestern United States but not Pennsylvania. They paid a tough price for their religion-based altruism.
Some members of the Native American Church made a ceremonial tea from peyote buttons (parts of a hallucinogenic cactus) covered with water and stored in a closed jar in the refrigerator for 2 months. Later, as part of religious practice, 13 church members ingested contents of the communal jar. Two to 4 days later, 3 of them developed botulism.28 Type B botulinum toxin was found in the peyote tea.
Atmospheric changes and natural disasters can produce dramatic alterations in disease prevalence and distribution. There seems to be a clear consensus in the scientific community that global warming is progressing. It is likely that atmospheric warming will expand the frequency and distribution of mosquito-borne diseases such as malaria, yellow fever, and dengue.29 Within the temperature ranges at which mosquitoes live, they reproduce faster and bite more often as the air becomes warmer, and the pathogens they carry also reproduce and mature at faster rates with increased heat. Global warming will enable mosquitoes to invade geographical areas previously devoid of these pests and the diseases they carry; models predict that by the end of the current century, warming will have enlarged the area for malaria transmission from one containing 45% of the world's population to one containing 60%.
In the aftermath of the December 2004 tsunami, 6 individuals in southern Thailand were diagnosed with pneumonia due to the bacterium Burkholderia pseudomallei, the cause of melioidosis, an illness which is not endemic in the region.30 All 6 victims had experienced near-drowning episodes and had aspirated water during the tsunami.
Hurricane Katrina made landfall on the Gulf Coast on August 29, 2005. During the following 2 weeks, 22 cases of Vibrio infections were reported in residents of Louisiana and Mississippi; 5 died.31 Most of these infections began as wound infections when cuts and abrasions were immersed in floodwaters.
Changes in society and the natural environment can affect patterns of disease. An appreciation of these changing patterns should be fostered as part of medical education. Illustrative true-life stories, like those presented in this discussion, can be used to spice up traditional lectures and encourage ways of thinking about diseases beyond the usual fact gathering. Interactive small group discussions can include anticipatory exercises. What health problems might be encountered when manned space flight becomes part of the fabric of everyday life? What would happen if a person with undiagnosed tuberculosis got on a space station and produced millions of infectious particles that remained suspended indefinitely in a zero-gravity environment?
Teaching about human illnesses in the context of societal and environmental change can foster creative thinking and better prepare physicians for the unexpected events that surely will come during their professionally active years. Besides, it is fun!
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