The inevitable risk borne by medical workers in the process of caring for patients with contagious diseases has been historically most apparent in epidemics, during which physicians have selflessly treated patients known to have dangerous, communicable infections. Investigators of infectious diseases still must face hazards when they work with microorganisms of uncertain danger and contagiousness, as exemplified by the death of Howard Ricketts in the study of typhus and the risks incurred by researchers working with HIV, the AIDS virus. Our knowledge of how infectious diseases are spread and the development of prudent infection control guidelines, however, have eliminated much of the risk for modern physicians. Physicians who follow accepted rules for patient isolation, acquire a basic knowledge of how infections are transmitted, and receive proper immunizations will set an example of responsible behavior for other medical and paramedical workers, and protect themselves and other patients from unnecessary hazard.

Transmission of Infectious Diseases

The four principal routes by which infections may be transmitted from patient to physician or vice versa form the basis of hospital infection control guidelines.

1. Contact transmission is the most important manner in which physicians may contract or spread infectious diseases. It may occur through direct physical contact (e.g., examining a wound), indirect contact through a formite (e.g., changing wound dressings or using a contaminated medical instrument), or droplet contact in which airborne infectious agents are spread short distances through coughing or sneezing. Most nosocomial infection with multiple-antibiotic-resistant bacteria, for example, derives from contact spread of microorganisms by physicians or staff.
2. Vehicular transmission involves contaminated objects, for example, food (salmonellosis), blood (hepatitis), water (legionellosis), or drugs and supplies (e.g., contaminated intravenous catheters or intravenous fluids and drugs).
3. Airborne transmission implies the dissemination of infectious particles suspended in air (e.g., tuberculosis), often for long distances.
4. Vector transmission, as through insect or animal spread, is more relevant to geographic medicine than clinical practice.

Other important microbial and clinical factors relating to the specific circumstances of the encounter between a physician and a patient also influence the "contagiousness," or likelihood of successful transmission, of an infectious disease. For example, large inoculum of organisms increases the chance of infection, regardless of the intrinsic capacity of an organism to cause human disease; hence, an otherwise harmless organism, when ingested in large numbers, may cause fever and vomiting (e.g., Bacillus cereus, a common cause of "food poisoning"). Microorganisms vary greatly among species, and even among strains within the same species (e.g., the highly variable disease that results from infection with the various strains of Escherichia coli), in their capacity to cause human disease and the severity or types of symptoms they cause. These characteristics are referred to as the virulence of an organism. The condition and state of immunity of the host are important; age, vaccination history, the presence of comorbid chronic diseases, previous encounters with that particular microorganism, the status of the host's immune system (e.g., leukemic patients), and the intactness of the usual defenses such as cough, free drainage of the urinary tract, healthy skin, and the presence of normal resident bacterial flora can determine whether infection occurs and how it is manifested.

The Centers for Disease Control recommends that hospitals use one of two isolation procedure systems: the traditional, disease-specific system or a newer category-specific system which groups together diseases that call for similar isolation precautions. Listed in Table 226.1 are most of the community-acquired adult contagious diseases that a physician might encounter in a general hospital, the usual infectious materials (important exceptions may occur, especially for immunocompromised hosts), and the usual type and duration of isolation. More detailed recommendations are found in the references at the end of this chapter. Many infectious diseases require no isolation: most fungal infections, arthropod-borne viral and rickettsial infections, most bronchitis and viral upper respiratory infections of adults, food poisoning, infectious mononucleosis, and most sexually transmitted diseases require little more than a commonsense approach to patient management.

Table 226.1

Infectious Diseases That May Be Spread by or Contracted by Physicians during Ordinary Patient Care Activities ^a.

The category-specific isolation precautions recommended by the Centers for Disease Control (CDC) are listed in Table 226.2. Individual hospitals may modify or supplement these guidelines to meet their own needs, and physicians should discuss modifications that may help meet a particular patient's needs with the hospital epidemiologist when appropriate. Isolation may be instituted by physician's order or, in some hospitals, by nurses or the infection control committee. It is usually discontinued after the illness or infectious lesion has resolved, the cultures that caused the institution of isolation are negative, or shortly after effective treatment has been instituted in some easy-to-treat community-acquired infections (e.g., meningococcal infections).

Table 226.2

Category-Specific Isolation Precautions Recommended by the Centers for Disease Control.

In 1987 the CDC recommended that all patients have a type of blood/body-fluid (B/BF) precautions, referred to as universal precautions, because history and examination cannot reliably identify patients infected with HIV or other bloodborne pathogens:

1. Barrier precautions (gloves, masks, eyewear, gowns) should be used routinely in the appropriate circumstances when contact with blood, tissue fluids, semen, or vaginal fluid is anticipated.
2. Hands should be washed after glove removal and contaminated skin washed after exposure.
3. Special precautions to prevent puncture injuries should be observed.
4. Mouth protection should be used for mouth-to-mouth resuscitation.
5. Contact with weeping skin lesions should be avoided.
6. Pregnant health care workers are at special risk and should be especially observant of all precautions.

Physicians are ethically obliged to follow isolation guidelines compulsively for the protection of their patients and themselves. Any lapses in following their own rules are acutely noted by other caregivers and the patient's family.

Isolation, it must be remembered, is not harmless. Elderly patients may become disoriented, all patients become depressed, friends are hesitant to visit, nursing care may suffer, and physicians become reluctant to touch patients or visit them as frequently after isolation procedures are instituted.

Nosocomial Infections

Hospital-acquired infections, defined as ones not present or incubating at hospital admission, occur in approximately 5% of admissions; older, immunocompromised patients, however, have a much higher incidence of nosocomial infection. When these infections occur, hospitalization is prolonged an average of 5 to 10 days, health care expenses are greatly increased, and the morbidity and mortality experienced from the primary illness are increased. Nosocomial infections are often caused by multiple-antibiotic-resistant organisms (e.g., pseudomonas, serratia, acinetobacter, enterobacter) that are rarely encountered in community-acquired infections; successful treatment of these organisms is more difficult, requiring complicated, expensive, and toxic antibiotic regimens.

Physicians, nurses, and other health care workers in the hospital are, to a large degree, responsible for the spread of these bacteria, permitting them to colonize the respiratory tracts, urinary tracts, and skin of patients who might otherwise be colonized with less virulent, more antibiotic-sensitive organisms. It is commonly observed, for example, that urinary infections often occur in clusters of patients infected with the same strain of multiple-antibiotic-resistant bacteria and that the only apparent epidemiologic connections between these patients are their physicians and nurses.

Compulsive handwashing after every patient is examined, whether they are known to be infected or not, is prudent. Patients with infected wounds, respiratory infections, cellulitis, decubitus ulcers, and urinary infections may be infected with virulent, multiple-antibiotic-resistant organisms. Table 226.2 lists the standard precautions that should be exercised for patients recognized as having a potentially contagious infection. Infected patients who have not been placed on isolation should be touched with caution, gloves or mask should be used when common sense dictates, and hands should be carefully washed before going to the next patient.

Protection of Health Care Workers from Infectious Diseases

While health care workers rarely contract infectious diseases from their patients, some infections represent a special risk, and vaccination, treatment, or surveillance is recommended; many hospitals, in fact, require some vaccinations to reduce employee absenteeism and protect employees and patients (such requirements result from the nearly universal poor compliance of hospital workers with reasonable recommendations).

References

1. American College of Physicians. Guide for adult immunization. 1985. [PubMed: 10269942]
2. Garner JS, Simmons BP. Guidelines for isolation precautions for use in hospitals. Am J Infect Control. 1984;12:103–13.
3. McCray E. Cooperative Needlestick Surveillance Group. Occupational risk of the acquired immunodeficiency syndrome among health care workers. N Engl J Med. 1986;314:1127–32. [PubMed: 3485769]
4. Patterson WB, Craven DE, Schwartz DA, Nardell EA, Kasmer J, Noble J. Occupational hazards of hospital personnel. Ann Intern Med. 1985;102:658–80. [PubMed: 3885818]
5. Recommendations for prevention of HIV transmission in health-care settings. MMWR. 1987;36:3S–17S. [PubMed: 3112554]
6. Recommendations for prevention of HIV transmission-in-healthcare-settings. Update: universal precautions for prevention of HIV, hepatitis B virus, and other bloodborne pathogens in healthcare settings. MMWR. 1988;37:377–88. [PubMed: 2836717]
7. Recommendations for prevention of HIV transmission-in-healthcare-settings. Update: AIDS and HIV infection among health care workers. MMWR. 1988;37:229–39.
8. Williams WW, Garner JS. Personnel health services. In: Bennet JV, Brachman PS, eds. Hospital infections. Boston: Little, Brown, 1986;17–38.