The good news is that a few simple precautions can prevent some disease transmission. For example, make sure you wash your hands frequently and thoroughly. Use soap and warm water and vigorously rub your hands together for at least 20 seconds. Washing your hands is the gold standard though! Dangerous organisms can thrive in improperly prepared food.
Avoid cross-contamination by keeping raw meats and produce separate. Use different preparation surfaces for raw meats and wash surfaces and utensils thoroughly.
Freeze or refrigerate perishable foods and leftovers promptly. When camping or enjoying wooded areas, wear long pants and long sleeves. Use insect repellent and mosquito netting. Stay up to date on vaccinations, especially when traveling. Vaccinations can drastically reduce your risk of becoming ill with some infectious diseases.
If you can avoid a particular disease, you can also prevent the spread of the disease. There are different types of vaccinations, such as those to prevent:.
Infectious diseases are caused by types of bacteria, viruses, parasites, and fungi around us. If you understand the transmission process, you can use this knowledge to protect yourself and help prevent the spread of illnesses.
A noncommunicable disease is a noninfectious health condition lasting for a long period of time. This is also known as a chronic disease…. Malaria is typically found in tropical and subtropical climates. You may have heard about being prescribed…. Around the globe, people who are immunosuppressed and at a higher risk for developing complications from COVID have been making their voices heard. New research finds that cells in the ear are susceptible to infection with SARS-CoV2, causing symptoms that include dizziness, ear ringing, and….
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People are renting pools via a new app this summer. Is this practice safe? There are hundreds of lymph nodes in the body that help fight infection, including the armpit.
Learn more about what it looks like when they're…. Request an Appointment at Mayo Clinic. What are superbugs and how can I protect myself from infection? Share on: Facebook Twitter. Show references Facts about infectious disease. Infectious Disease Society of America.
Accessed May 29, Jameson JL, et al. Approach to the patient with an infectious disease. In: Harrison's Principles of Internal Medicine. New York, N. Clean hands count for safe health care. Centers for Disease Control and Prevention. Kumar P, et al. Infectious diseases and tropical medicine. In: Kumar and Clark's Clinical Medicine.
Philadelphia, Pa. LaRocque R, et al. Causes of infectious diarrhea and other foodborne illnesses in resource-rich settings. Ryan KJ, ed. Infectious diseases: Syndromes and etiologies. In: Sherris Medical Microbiology. File TM, et al. Epidemiology, pathogenesis, and microbiology of community-acquired pneumonia in adults. Accessed May DeClerq E, et al.
Approved antiviral drugs over the past 50 years. Clinical Microbiology Reviews. Mousa HAL. The malaria resistance afforded carriers of the sickle cell trait exemplifies how genetics can influence susceptibility to infectious disease Aidoo et al. Susceptibility is also affected by extremes of age, stress, pregnancy, nutritional status, and underlying diseases.
Mechanical and chemical surface barriers such as the skin, the flushing action of tears, and the trapping action of mucus are the first host obstacles to infection.
For example, wound infection and secondary sepsis are serious complications of severe burns which remove the skin barrier to microbial entry. Lysozyme, secreted in saliva, tears, milk, sweat, and mucus, and gastric acid have bactericidal properties, and vaginal acid is microbicidal for many agents of sexually transmitted infections STIs. Microbiome-resident bacteria a. The innate and adaptive immune responses are critical components of the host response to infectious agents Table 1.
Each of these responses is carried out by cells of a distinct hematopoietic stem cell lineage: the myeloid lineage gives rise to innate immune cells e. The innate immune response is an immediate, nonspecific response to broad groups of pathogens.
By contrast, the adaptive immune response is initially generated over a period of 3—4 days, it recognizes specific pathogens, and it consists of two main branches: 1 T cell-mediated immunity a. The innate and adaptive responses also differ in that the latter has memory, whereas the former does not. As a consequence of adaptive immune memory , if an infectious agent makes a second attempt to infect a host, pathogen-specific memory T cells, memory B cells, and antibodies will mount a secondary immune response that is much more rapid and intense than the initial, primary response and, thus, better able to inhibit infection and disease.
Immune memory is the basis for the use of vaccines that are given in an attempt to stimulate an individual's adaptive immune system to generate pathogen-specific immune memory. Of note, in some cases the response of the immune system to an infectious agent can contribute to disease progress. For example, immunopathology is thought to be responsible for the severe acute disease that can occur following infection with a dengue virus that is serotypically distinct from that causing initial dengue infection Screaton et al.
An immune host is someone protected against a specific pathogen because of previous infection or vaccination such that subsequent infection will not take place or, if infection does occur, the severity of disease is diminished.
The duration and efficacy of immunity following immunization by natural infection or vaccination varies depending upon the infecting agent, quality of the vaccine, type of vaccine i. For example, a single yellow fever vaccination appears to confer lifelong immunity, whereas immune protection against tetanus requires repeat vaccination every 10 years Staples et al. In malaria-endemic areas, natural immunity to malaria usually develops by 5 years of age and, while protective from severe disease and death, it is incomplete and short-lived Langhorne et al.
Functionally, there are two basic types of immunization, active and passive. Active immunization refers to the generation of immune protection by a host's own immune response. In contrast, passive immunization is conferred by transfer of immune effectors, most commonly antibody a. For example, after exposure to a dog bite, an individual who seeks medical care will receive both active and passive postexposure immune prophylaxis consisting of rabies vaccine to induce the host immune response and rabies immune globulin to provide immediate passive protection against rabies.
An example of natural passive immunization is the transfer of immunity from mother to infant during breastfeeding. Vaccination does not always result in active immunization; failure of vaccination can be due to either host or vaccine issues.
Individuals who are immunosuppressed as, for example, a result of HIV infection, malnutrition, immunosuppressive therapy, or immune senescence might not mount a sufficient response after vaccination so as to be adequately immunized protected.
Similarly, vaccination with an inadequate amount of vaccine or a vaccine of poor quality e. Environmental determinants of vulnerability to infectious diseases include physical, social, behavioral, cultural, political, and economic factors. In some cases, environmental influences increase risk of exposure to an infectious agent. For example, following an earthquake, environmental disruption can increase the risk of exposure to Clostridium tetani and result in host traumatic injuries that provide portals of entry for the bacterium.
Environmental factors promoting vulnerability can also lead to an increase in susceptibility to infection by inducing physiological changes in an individual. For example, a child living in a resource-poor setting and vulnerable to malnutrition may be at increased risk of infection due to malnutrition-induced immunosuppression. WASH, water, sanitation, and hygiene; E. A unique characteristic of many infectious diseases is that exposure to certain infectious agents can have consequences for other individuals, because an infected person can act as a source of exposure.
Some pathogens e. From a public health standpoint, it is useful to define stages of an infectious disease with respect to both clinical disease and potential for transmission Figure 3. With respect to disease, the incubation period is defined as the time from exposure to an infectious agent until the time of first signs or symptoms of disease. The incubation period is followed by the period of clinical illness which is the duration between first and last disease signs or symptoms.
With respect to transmission of an infectious agent, the latent preinfectious period is the duration of time between exposure to an agent and the onset of infectiousness. It is followed by the infectious period a. In parasitic infections, the latent and infectious periods are commonly referred to as the prepatent period and patent period , respectively. Stages of infectious disease. The stages of an infectious disease can be identified with relation to signs and symptoms of illness in the host incubating and clinically ill , and the host's ability to transmit the infectious agent latent and infectious.
The red bar indicates when an individual is infectious but asymptomatic. The relationship between stages is an important determinant of carrier states and, thus, the ease of spread of an infectious disease through a population. The duration of disease stages is unique for each type of infection and it can vary widely for a given type of infection depending upon agent, host, and environmental factors that affect, for example, dose of the inoculated agent, route of exposure, host susceptibility, and agent infectivity and virulence.
Knowledge of the timing of disease stages is of key importance in the design of appropriate control and prevention strategies to prevent the spread of an infectious disease. For example, efforts to control the recent Ebola West Africa outbreak through contact tracing and quarantine were based on knowledge that the infectious period for Ebola does not begin until the start of the period of clinical illness, which occurs up to 21 days following exposure Figure 3 a ; Pandey et al.
A carrier is, by definition, an infectious individual who is not showing clinical evidence of disease and, thus, might unknowingly facilitate the spread of an infectious agent through a population. Incubatory carriers exist when the incubation period overlaps with the infectious period, as can occur in some cases of chicken pox Figure 3 b.
Convalescent carriers occur when the period of infectiousness extends beyond the period of clinical illness Figure 3 c. Carriers of this type can be a significant issue in promoting the spread of certain enteric infections, such as those caused by the bacterium, V. Healthy carriers , infected individuals that remain asymptomatic but are capable of transmitting an infectious agent, occur commonly with many infectious diseases e.
A variety of terms are used to describe the occurrence of an infectious disease within a specific geographic area or population. Sporadic diseases occur occasionally and unpredictably, while endemic diseases occur with predictable regularity. Levels of endemicity can be classified as holoendemic , hyperendemic , mesoendemic , or hypoendemic depending upon whether a disease occurs with, respectively, extreme, high, moderate, or low frequency.
For some infectious diseases, such as malaria, levels of endemicity are well defined and used as parameters for identifying disease risk and implementing control activities. An epidemic refers to an, often acute, increase in disease cases above the baseline level. An epidemic may reflect an escalation in the occurrence of an endemic disease or the appearance of a disease that did not previously exist in a population.
The term outbreak is often used synonymously with epidemic but can occasionally refer to an epidemic occurring in a more limited geographical area; for example, a foodborne illness associated with a group gathering. By contrast, a pandemic is an epidemic that has spread over a large geographic region, encompassing multiple countries or continents, or extending worldwide.
Influenza commonly occurs as a seasonal epidemic, but periodically it gives rise to a global pandemic, as was the case with H1N1 influenza.
Two fundamental measures of disease frequency are prevalence and incidence. Prevalence is an indicator of the number of existing cases in a population as it describes the proportion of individuals who have a particular disease, measured either at a given point in time point prevalence or during a specified time period period prevalence.
In contrast, incidence a. In some circumstances, a secondary attack rate is calculated to quantify the spread of disease to susceptible exposed persons from an index case the case first introducing an agent into a setting in a circumscribed population, such as in a household or hospital.
It is defined as the average number of secondary cases generated by a single, infectious case in a completely susceptible population.
Thus, a more accurate reflection of the potential for community disease spread is the effective reproductive number R which measures the average number of new infections due to a single infection. Herd immunity a. As a result of herd immunity, susceptible individuals who are not immune themselves are indirectly protected from infection Figure 4.
Vaccine hesitancy, the choice of individuals or their caregivers to delay or decline vaccination, can lead to overall lower levels of herd immunity.
Outbreaks of measles in the United States, including a large measles outbreak at an amusement park in California, highlight the phenomena of vaccine refusal and associated increased risk for vaccine-preventable diseases among both nonvaccinated and fully vaccinated but not fully protected individuals Phadke et al.
Herd immunity occurs when one is protected from infection by immunization occurring in the community. Using influenza as an example, the top box shows a population with a few infected individuals shown in red and the rest healthy but unimmunized shown in blue ; influenza spreads easily through the population. The middle box depicts the same population but with a small number who are immunized shown in yellow ; those who are immunized do not become infected, but a large proportion of the population becomes infected.
In the bottom box, a large proportion of the population is immunized; this prevents significant transmission, including to those who are unimmunized. The proportion that needs to be immunized depends on the pathogen Table 3. Thus, Ro and R can be used to calculate the target immunization coverage needed for the success of vaccination programs.
Proper diagnosis of infectious illnesses is essential for both appropriate treatment of patients and carrying out prevention and control surveillance activities. Two important properties that should be considered for any diagnostic test utilized are sensitivity and specificity. A test that is very sensitive is more likely to pick up individuals with the disease and possibly some without the disease ; a very sensitive test will have few false negatives.
Often, screening tests are highly sensitive to capture any possible cases , and confirmatory tests are more specific to rule out false-positive screening tests. Broadly, laboratory diagnosis of infectious diseases is based on tests that either directly identify an infectious agent or provide evidence that infection has occurred by documenting agent-specific immunity in the host Figure 5.
Identification of an infecting agent involves either direct examination of host specimens e. The main categories of analyses used in pathogen identification can be classified as phenotypic , revealing properties of the intact agent, nucleic acid-based , determining agent nucleic acid DNA or RNA characteristics and composition, and immunologic , detecting microbial antigen or evidence of immune response to an agent Figure 5. Cultured material containing large quantities of agent can undergo analyses to determine characteristics, such as biochemical enzymatic activity enzymatic profile and antimicrobial sensitivity , and to perform phage typing , a technique which differentiates bacterial strains according to the infectivity of strain-specific bacterial viruses a.
The ability of pathogen-specific PCR primers to generate an amplification product can confirm or rule out involvement of a specific pathogen.
Sequencing of amplified DNA fragments can also assist with pathogen identification. Most recently, next-generation sequencing technologies have made whole-genome sequencing a realistic subtyping method for use in foodborne outbreak investigation and surveillance Deng et al. The objective of immunologic analysis of specimens is to reveal evidence of an agent through detection of its antigenic components with agent-specific antibodies.
Serotyping refers to the grouping of variants of species of bacteria or viruses based on shared surface antigens that are identified using immunologic methodologies such as enzyme-linked immunosorbent assay ELISA and Western blotting. Methods of infectious disease diagnosis.
Laboratory methods for infectious disease diagnosis focus on either analyzing host specimens or environmental samples for an agent upper section , or analyzing the host for evidence of immunity to an agent lower section.
Closed solid bullets, category of test; open bullets, examples of tests. Immunologic assays are also used to look for evidence that an agent-specific immune response has occurred in an exposed or potentially exposed individual. Serologic tests detect pathogen-specific B cell—secreted antibodies in serum or other body fluids.
Some serologic assays simply detect the ability of host antibodies to bind to killed pathogen or components of pathogen e. Others rely on the ability of antibodies to actually neutralize the activity of live microbes; as, for example, the plaque reduction neutralization test which determines the ability of serum antibodies to neutralize virus.
Antibody titer measures the amount of a specific antibody present in serum or other fluid, expressed as the greatest dilution of serum that still gives a positive test in whatever assay is being employed. Intradermal tests for identification of T cell—mediated immediate type Type I hypersensitivity or delayed type Type IV hypersensitivity responses to microbial antigen can be used to diagnose or support the diagnosis of some bacterial, fungal, and parasitic infections, such as, the Mantoux tuberculin test for TB.
Based on the classic model of Leavell and Clark , infectious disease prevention activities can be categorized as primary, secondary, or tertiary. Primary prevention occurs at the predisease phase and aims to protect populations, so that infection and disease never occur. For example, measles immunization campaigns aim to decrease susceptibility following exposure. The goal of secondary prevention is to halt the progress of an infection during its early, often asymptomatic stages so as to prevent disease development or limit its severity; steps important for not only improving the prognosis of individual cases but also preventing infectious agent transmission.
For example, interventions for secondary prevention of hepatitis C in injection drug user populations include early diagnosis and treatment by active surveillance and screening Miller and Dillon, Tertiary prevention focuses on diseased individuals with the objective of limiting impact through, for example, interventions that decrease disease progression, increase functionality, and maximize quality of life.
Broadly, public health efforts to control infectious diseases focus on primary and secondary prevention activities that reduce the potential for exposure to an infectious agent and increase host resistance to infection. The objective of these activities can extend beyond disease control , as defined by the Dahlem Workshop on the Eradication of Infectious Diseases, to reach objectives of elimination and eradication Dowdle, ; Box 1.
As noted earlier, the causation and spread of an infectious disease is determined by the interplay between agent, host, and environmental factors. For any infectious disease, this interplay requires a specific linked sequence of events termed the chain of infection or chain of transmission Figure 6. The chain starts with the infectious agent residing and multiplying in some natural reservoir ; a human, animal, or part of the environment such as soil or water that supports the existence of the infectious agent in nature.
The infectious agent leaves the reservoir via a portal of exit and, using some mode of transmission , moves to reach a portal of entry into a susceptible host. A thorough understanding of the chain of infection is crucial for the prevention and control of any infectious disease, as breaking a link anywhere along the chain will stop transmission of the infectious agent.
Often more than one intervention can be effective in controlling a disease, and the approach selected will depend on multiple factors such as economics and ease with which an intervention can be executed in a given setting. It is important to realize that the potential for rapid and far-reaching movement of infectious agents that has accompanied globalization means that coordination of intervention activities within and between nations is required for optimal prevention and control of certain diseases.
The chain of infection a. One way to visualize the transmission of an infectious agent though a population is through the interconnectedness of six elements linked in a chain. Public health control and prevention efforts focus on breaking one or more links of the chain in order to stop disease spread.
The cause of any infectious disease is the infectious agent. As discussed earlier, many types of agents exist, and each can be characterized by its traits of infectivity, pathogenicity, and virulence.
A reservoir is often, but not always, the source from which the agent is transferred to a susceptible host. For example, bats are both the reservoir for Marburg virus and a source of infection for humans and bush animals including African gorillas. However, because morbidity and mortality due to Marburg infection is significant among these bush animals, they cannot act as a reservoir to sustain the virus in nature they die too quickly , although they can act as a source to transmit Marburg to humans.
Infectious agents can exist in more than one type of reservoir. The number and types of reservoirs are important determinants of how easily an infectious disease can be prevented, controlled, and, in some cases, eliminated or eradicated. Animal, particularly wild animal, reservoirs, and environmental reservoirs in nature can be difficult to manage and, thus, can pose significant challenges to public health control efforts.
In contrast, infectious agents that only occur in human reservoirs are among those most easily targeted, as illustrated by the success of smallpox eradication. Humans are the reservoir for many common infectious diseases including STIs e. Humans also serve as a reservoir, although not always a primary reservoir, for many neglected tropical diseases NTDs as, for example, dracunculiasis a. Guinea worm. From a public health standpoint, an important feature of human reservoirs is that they might not show signs of illness and, thus, can potentially act as unrecognized carriers of disease within communities.
The classic example of a human reservoir is the cook Mary Mallon Typhoid Mary ; an asymptomatic chronic carrier of Salmonella enterica serovar Typhi who was linked to at least 53 cases of typhoid fever Soper, Animals are a reservoir for many human infectious diseases. Zoonosis is the term used to describe any infectious disease that is naturally transmissible from animals to humans. Zoonotic reservoirs and sources of human disease agents include both domestic companion and production animals e.
Control and prevention of zoonotic diseases requires the concerted efforts of professionals of multiple disciplines and is the basis for what has become known as the One Health approach Gibbs, This approach emphasizes the interconnectedness of human health, animal health, and the environment and recognizes the necessity of multidisciplinary collaboration in order to prevent and respond to public health threats.
Inanimate matter in the environment, such as soil and water, can also act as a reservoir of human infectious disease agents. The causative agents of tetanus and botulism Clostridium tetani and C.
Legionella pneumophila , the etiologic agent of Legionnaires' disease, is part of the natural flora of freshwater rivers, streams, and other bodies. However, the pathogen particularly thrives in engineered aquatic reservoirs such as cooling towers, fountains, and central air conditioning systems, which provide conditions that promote bacterial multiplication and are frequently linked to outbreaks. Soil and water are also sources of infection for several protozoa and helminth species which, when excreted by a human reservoir host, can often survive for weeks to months.
Outbreaks of both cryptosporidiosis and giardiasis commonly occur during summer months as a result of contact with contaminated recreational water. Soil containing roundworm Ascaris lumbricoides eggs is an important source of soil-transmitted helminth infections in children. Central to these interventions are surveillance activities that routinely identify disease agents within reservoirs. When humans are the reservoir, or source, of an infectious agent, early and rapid diagnosis and treatment are key to decreasing the duration of infection and risk of transmission.
Both active surveillance and passive surveillance are used to detect infected cases and carriers. Some readily communicable diseases, such as Ebola, can require isolation of infected individuals to minimize the risk of transmission. As part of the global effort to eradicate dracunculiasis, several endemic countries have established case containment centers to provide treatment and support to patients with emerging Guinea worms to keep them from contaminating water sources and, thereby, exposing others Hochberg et al.
Contact tracing and quarantine are other activities employed in the control of infections originating from a human reservoir or source. During the West Africa Ebola outbreak, key control efforts focused on the tracing and daily follow-up of healthy individuals who had come in contact with Ebola patients and were potentially infected with the virus Pandey et al.
One Health emphasizes the importance of surveillance and monitoring for zoonotic pathogens in animal populations. For some diseases e. Once animal reservoirs and sources of infection are identified, approaches to prevention and control include reservoir elimination and prevention of reservoir infection.
The focus of prevention and control activities for these diseases reflects the extent to which a zoonotic pathogen has evolved to become established in human populations Wolfe et al.
For some zoonotic diseases e. Currently, most human cases of avian influenza are the result of human infection from birds; human-to-human transmission is extremely rare.
Thus, reservoir elimination by culling infected poultry flocks is a recommended measure for controlling avian influenza in birds and preventing sporadic infection of humans CDC, Other zoonotic diseases demonstrate varying degrees of secondary human-to-human transmission following primary transmission a. Both rates of spillover and the ability to sustain human-to-human transmission can vary widely between zoonoses and, in consequence, control strategies can also be quite different.
For example, outbreaks of Ebola arise following an initial bush animal-to-human transmission event, and subsequent human-to-human transmission is often limited Feldmann and Geisbert, Thus, while Ebola outbreak prevention efforts would include limiting contact with bush animals, such efforts would not be useful for prevention of dengue outbreaks.
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