Prevention of Infectious Diseases

20 Prevention of Infectious Diseases

I Overview of Infectious Disease

Humans have coexisted with microbes since the beginning of the human race. One of the originators of epidemiology, John Snow, laid the foundations of the discipline by analyzing and controlling cholera, a bacterial disease caused by Vibrio cholerae. Immunity to infection is influenced by a person’s genetic background, overall health, access to good sanitation and nutrition, and even social status. Therefore, the prevalence of infectious diseases is a good proxy for disenfranchisement and poverty in a population. Poverty plays multiple roles in the cycle of infectious diseases. Poverty can contribute to infectious diseases by making the environment more suitable for disease transmission, and poverty can also be a consequence of infectious diseases. Causal pathways include complications of pregnancy, repeated episodes of diarrheal illness in children leading to slowed mental and physical development, and the death of broad swaths of a parent generation (e.g., from AIDS).1

Control of infectious disease is challenging because of the adaptive capabilities of microbes. Microbes have inhabited the earth far longer than humans and have successfully adapted to all evolutionary challenges. Several recent developments fuel a global environment in which new infectious diseases emerge and become rooted in society, as summarized by the Institute of Medicine into the convergence model2 (Fig. 20-1; see also Chapter 30). The convergence model is centered on the human-microbe interaction. The black box in the center of the figure indicates that these interactions can be difficult to predict in an emerging disease. More importantly, a microbe is a necessary but not sufficient cause of ill health. Humans constantly encounter millions of potentially harmful microbes without falling ill. Four domains of factors impact humans and microbes or their interactions. Each of these factors provides a starting point for thinking systematically about pathways of prevention (Box 20-1).

Box 20-1 Four Domains of Human-Microbe Interaction

Pathways in Prevention of Infectious Disease

Understanding and controlling infectious diseases requires integrating many different preventive and public health skills. These include obtaining accurate history on sensitive topics such as sexual behaviors; geographic epidemiology; outbreak investigation; analysis of disease rates by different variables (age, gender, race, socioeconomic status) to detect high-risk groups; successful outreach to public and health professionals; screening; contact tracing; immunization; school health; counseling; sanitation; waste and wastewater management; food protection; disease registries; and prophylactic drugs. Diseases vary, but the epidemiologic skills are similar for different diseases, independent of their mode of transmission (e.g., STD vs. vector-borne disease). Public health controls disease through prevention efforts in three broad categories, as follows2:

All infection control activity requires a thorough understanding of the various infectious diseases. This chapter only briefly addresses the complexity of different diseases, and important diseases are discussed elsewhere (e.g., see Chapter 3 for influenza and Select Readings for further information). On the other hand, control of an infectious disease often only requires understanding how it is transmitted. For example, John Snow determined that water from a particular company caused most of the cholera in London. Armed with this understanding and the supporting data, he was able to convince the local council to disable the well. Breaking the chain of transmission helped end the outbreak.

Diseases can be usefully grouped according to transmission3 (Table 20-1). Often, surveys of patients and “shoe leather” epidemiology will reveal the mode of transmission, and public health officials can disrupt disease transmission before the causative agent has been identified (see Chapter 3).

A Burden of Disease

Infectious diseases affect all countries, but the burden of disease is different in developed and developing countries. In the United States, infectious disease mortality has for the most part steadily declined since the early 1900s.4 Most of this decline preceded the availability of antibiotics or vaccines and was likely the result of better hygiene, sanitation, and chlorination of drinking water.

Since the 1980s, the burden of infectious disease in the United States has again increased, largely because of emerging or reemerging infections, such as multidrug-resistant Staphylococcus aureus, Clostridium difficile, and Mycobacterium tuberculosis. Globally, infectious diseases account for about half the disease burden in low-income and middle-income countries. Infectious diseases especially impact children; more than half of childhood mortality is attributable to acute respiratory infections, measles, diarrheal illnesses, malaria, and human immunodeficiency virus and acquired immunodeficiency syndrome (HIV/AIDS).

To weigh the effects of disease on life span, many global health experts measure the impact of infectious disease in disability-adjusted life years (DALY). DALY take into account premature mortality and years of life lived in less than full health (see Chapter 24.) Five of the 10 leading diseases for global disease burden are infectious: HIV/AIDS, lower respiratory infections, diarrheal illnesses, malaria, and tuberculosis (TB). More importantly, many of the infectious diseases causing a large disease burden are increasing (HIV/AIDS, respiratory diseases) and are disproportionately impacting the lowest-income countries.5

See online Figure 20-2 on for global mortality rates by cause and region. image

Worldwide death rates from malaria and HIV/AIDS are increasing. These increases have negated gains derived from reduced child mortality from measles, acute respiratory infections, and diarrhea.

B Obtaining an Accurate History

Transmission of major infectious diseases often results from a person’s behavior, including eating and hygiene habits, pets in residence, illicit drug use, and sexual partners. Therefore, caring for a patient with an infectious disease requires taking a careful behavioral history. The behaviors resulting in transmission can be mainstream and unrelated to any social taboos, such as the restaurant visited before a diarrheal illness.

More often, patients may be embarrassed by behavior that induced the infectious disease. Examples range from people kissing their pets (leading to transmission of Pasteurella spp.6) to sexual behaviors and use of illicit drugs (leading to transmission of sexually transmitted and blood-borne diseases). Patients may not be comfortable sharing such information unless the clinician is skilled at putting people at ease and asks about intimate details in a nonjudgmental way. Taking such a history is crucial for understanding how the patient contracted the infectious disease and who else may have been infected.

Client-centered counseling means tailoring prevention messages to a patient’s practices, values, and risk perceptions. For sexually transmitted diseases (STDs), or sexually transmitted infections (STIs), client-centered counseling has been shown to increase the likelihood of patients changing their behavior.7 The same likely holds true for other behaviors. As in other areas of counseling, it is important that the clinician start with open-ended questions and reassure the patient that the information will be treated confidentially.

Counseling for STDs is discussed in detail here for several reasons. STDs play a major role in infectious disease epidemiology, have a significant impact on fertility and pregnancy outcomes, and also may cause problems in newborns (e.g., syphilis, gonorrhea). Women are often more vulnerable to STDs than men, which poses particular challenges, because many effective interventions require male condoms. Also, effective counseling for STDs has been extensively researched, but many clinicians are uncomfortable addressing this topic.

Counseling for STDs can serve as a template for other sensitive topics, such as illicit drug use, risk taking among adolescents, and addiction. For STDs and other sensitive topics, it is particularly important that the interviewing techniques be culturally appropriate and, especially with adolescents, correspond to patients’ developmental levels. The interview should begin with more neutral topics in the social history (e.g., sports, activities, diet), then move to questions about sexual behaviors. In broaching such topics, it is important to frame the questions, as in the following examples:

Additional information on effective STD counseling and behavioral interventions can be found online.9

II Public Health Priorities

A HIV/AIDS, Tuberculosis, and Malaria

In some countries in sub-Saharan Africa, HIV/AIDS, tuberculosis, and malaria together account for more than 50% of deaths.10 These illnesses decrease health and constrain growth and development of many of the poorest nations. In general, they also impact developed countries, either internally through income inequality or externally through immigration and international travel. All these diseases have important lessons to offer for successful infectious disease prevention. Prevention efforts for these three diseases are often implemented together, as through the Global Fund to Fight AIDS, Tuberculosis, and Malaria.11 The Global Fund follows an innovative model, targeting all three diseases through partnerships among government, civil society, the private sector (including businesses and foundations), and affected communities, combined with meticulous attention to data and evaluation.

1 Human Immunodeficiency Virus/Acquired Immunodeficiency Syndrome


No new disease in modern times has had as severe an impact worldwide as AIDS, which is caused by the human immunodeficiency virus. Although HIV transmission and management are of major concern in the United States, the situation is more serious in Southeast Asia, South America, Russia, and the Indian subcontinent. It is catastrophic in sub-Saharan Africa, where many adults are infected, death rates in the most productive age groups are extremely high, and many children have been orphaned. In 2009 an estimated 2.6 million people became newly infected with HIV, with 1.8 million deaths worldwide.12

The U.S. Centers for Disease Control and Prevention (CDC) estimated in 2012 that more than 1 million people are living with HIV infection in the United States, with around 18,000 deaths annually. An estimated 50,300 Americans are newly infected with HIV each year;13 one in five people (21%) living with HIV are unaware of having the infection, presumably accounting for a large proportion of new infections.

Prevention of HIV Infection and AIDS

The best ways to prevent the spread of HIV/AIDS have been known since the syndrome was discovered and before the responsible microorganism was identified. They consist of restricting sexual activity to a monogamous relationship and avoiding IDU. If a person chooses to have multiple sexual partners or to use intravenous drugs, the next best prevention is to use condoms for every sexual contact and clean needles and equipment for each IDU episode. Male circumcision, antiretroviral therapy (ART) and possibly also antiretroviral vaginal gel can also significantly decrease infection rates.14 Treatment is prevention (see below).

Globally, an unprecedented coalition of governments, nongovernmental organizations (NGOs), pharmaceutical companies, and private foundations have worked together successfully to control the spread of the AIDS epidemic. Through these efforts, the annual number of new HIV infections has declined worldwide, and AIDS-related deaths have fallen with increased access to ART. In 33 countries (22 in sub-Saharan Africa) the HIV incidence decreased more than 25% between 2001 and 2009.15 These successes highlight the following lessons about prevention and disease control in general:

Infected patients may change their behavior to protect others if they know they are infected. For this reason, anonymous HIV testing centers have been established in most U.S. areas. However, these testing centers identify less HIV infection than other health care settings, so preventive counseling and testing has shifted over the last 10 years. The changes emphasize ease of access to testing.

The CDC recommends routine, voluntary, opt-out HIV screening for all patients age 13 to 64 in health care settings, unless prevalence of undiagnosed HIV infection has been documented at less than 0.1%.16 Box 20-2 provides additional CDC guidelines.16,17

Aug 27, 2016 | Posted by in PUBLIC HEALTH AND EPIDEMIOLOGY | Comments Off on Prevention of Infectious Diseases

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