Leon gordis epidemiology 6th edition pdf free download

With extensive treatment of the heart of epidemiology - from study designs to descriptive epidemiology to quantitative measures - this reader-friendly text is accessible and interesting to a wide range of beginning students in all health-related disciplines. A unique focus is given to real-world applications of epidemiology and the development of skills that students can apply in subsequent course work and in the field. The text is also accompanied by a complete package of instructor and student resources available through a companion Web site.

It is aimed both at researchers and general readers of the often confusing scholarly literature on the subject. Heesterbeek Centre for Biometry Wageningen, The Netherlands The mathematical modelling of epidemics in populations is a vast and important area of study. It is about translating biological assumptions into mathematics, about mathematical analysis aided by interpretation and about obtaining insight into epidemic phenomena when translating mathematical results back into population biology.

Model assumptions are formulated in terms of, usually stochastic, behaviour of individuals and then the resulting phenomena, at the population level, are unravelled. Conceptual clarity is attained, assumptions are stated clearly, hidden working hypotheses are attained and mechanistic links between different observables are exposed. In literally working through this text, the reader acquires modelling skills that are also valuable outside of epidemiology, certainly within population dynamics, but even beyond that.

In addition, the reader receives training in mathematical argumentation. The text is aimed at applied mathematicians with an interest in population biology and epidemiology, at theoretical biologists and epidemiologists. Previous exposure to epidemic concepts is not required, as all background information is given. The book is primarily aimed at self-study and ideally suited for small discussion groups, or for use as a course text.

Epidemic is defined The first clinical trial, Cardiovascular Risk Reduction by as the occurrence in a community or region of a group Early Anemia Treatment with Epoetin Beta CREATE ,3 of illnesses of similar nature, clearly in excess of normal showed that early and complete correction of anemia expectancy and derived from a common or a propagated to a target hemoglobin level in the normal range source Fig.

Pandemic refers to a worldwide failed to reduce the incidence of cardiovascular events epidemic. The How do we know when we have an excess over second trial, Correction of Hemoglobin and Outcomes what is expected? There is no precise answer to either question. As a result, in , the US Food and Drug Adminis- Two examples will show how pandemics and fear tration issued a black box warning adding significant of pandemics relate to the development of public restrictions on the use of ESAs.

Patients with chronic kidney disease are often includes the following: 1 prescribers should use the anemic, which is commonly corrected by injection lowest dose of ESA that will gradually increase the of erythropoiesis-stimulating agents ESAs ; these are hemoglobin concentration to the lowest level sufficient genetically engineered forms of the human erythro- to avoid the need for red blood cell transfusion and poietin hormone.

Although transmission of concerns about the safety of using ESAs for anemia naturally occurring H5N1 has been primarily limited correction to optimal levels in patients with chronic to persons having direct contact with infected animals, kidney disease, as neither study anticipated these results. Primary composite end point 0. Correction of anemia with epoetin alfa in chronic kidney disease. N Engl J Med. Wisconsin-Madison in the United States, created geneti- cally altered H5N1 strains that could be transmitted between mammals ferrets through the air.

After reviewing the two studies, the US National Science Advisory Board for Biosecurity, for the first time in its history, recommended against publishing the details of the methodologies used in these studies. Other scientists, however, including members of an expert panel assembled by the World Health Organiza- tion WHO , disagreed, stating that the work was important to public health efforts to prevent a possible Fig.

The results of the two studies were subsequently published in May and June of There has therefore been serious benefits to society from the results of these types of concern that certain mutations in the virus might studies outweigh the risks from the uncontrolled spread increase transmissibility of the virus to humans and of mutated virus, resulting from either lapses in biosafety could therefore result in a human pandemic.

In order in the laboratory accidental release of the virus or to understand fully the possibility of such a mutation bioterrorist activity intentional release of the virus. Globally, norovirus freedom in science remain highly relevant issues today. If an outbreak occurs in the group cruise ships. The Centers for Disease Control and of people who have eaten the food, it is called a common- Prevention CDC has reported that rates of AGE among vehicle exposure, because all the cases that occurred passengers on cruise ships have decreased from The food may be served only once—for example, while the rate among crew members was essentially at a catered luncheon—resulting in a single exposure to unchanged.

The epidemiologic picture aboard these ships. In areas with a high prevalence of norovirus, For purposes of this discussion, we will focus on particularly the recombinant GII.

What are the characteristics of such an on December 14, , a student in third grade vomited outbreak? First, such outbreaks are generally explosive— in the classroom and washroom several times and was that is, there is a sudden and rapid increase in the considered the earliest suspected case of norovirus. Interestingly, single-exposure common-vehicle which were mainly located on the fourth floor 12 epidemics of noncommunicable diseases, such as the cases and third floor 9 cases of the school building.

The first peak of the outbreak was to follow the same pattern. Second, the cases are limited on December 17, which was starting to taper off when to people who share the common exposure. This is implementation of control measures such as quarantine self-evident, because in the first wave of cases we would and disinfection were followed.

However, a few days not expect the disease to develop in people who were later, on December 25, the attack rate peaked again, not exposed unless there was another independent with cases occurring mainly on the second floor 12 source of the disease in the community. Third, in a cases and third floor 5 cases. In order to aggressively food-borne outbreak, cases rarely occur in persons who contain the outbreak, the school was closed temporarily did not eat the food—that is, those who acquire the and the outbreak came to an end on December The reason for the relative rarity of such secondary cases Immunity and Susceptibility in this type of outbreak is not well understood.

The presence of a large proportion of immune 8 persons in the population lessens the likelihood that 6 a person with the disease will come into contact with 4 a susceptible individual. We can achieve onset in a school in the province of in Jiangsu Province, China, in highly effective protection by immunizing a large part An acute gastroenteritis outbreak of the population; the remaining part will be protected caused by GII.

Int J Infect Dis. For herd immunity to exist, certain conditions must be met. The disease agent must be restricted to a single who are susceptible and therefore at risk for the disease host species within which transmission occurs, and and the number of people who are not susceptible or that transmission must be relatively direct from one immune and therefore not at risk.

They may be immune member of the host species to another. If we have a because they have had the disease previously and have reservoir in which the organism can exist outside the antibodies or because they have been immunized. They human host, herd immunity will not operate because also may not be susceptible on a genetic basis.

Clearly other means of transmission may be available. In addi- if the entire population is immune, no epidemic can tion, infections must induce solid immunity. If immunity develop. But the balance is usually struck somewhere is only partial, we will not build up a large proportion in between immunity and susceptibility, and when of immune people in the community.

Herd immunity operates if outbreak increases. For example, in the 19th century, Panum is the same. But if a person is infected and all of his observed that measles occurred in the Faroe Islands or her interactions are with people who are susceptible in epidemic form when infected individuals entered i.

Herd immunity operates optimally when developed when new susceptible recruits arrived at the populations are constantly mixing together. This is a Great Lakes Naval Station. All of us associate with family and friends, for example, more than we Herd Immunity do with strangers.

However, the degree to which herd Herd immunity is defined as the resistance of a group immunity is achieved depends on the extent to which of people to an attack by a disease to which a large the population approaches a random mixing. Thus we proportion of the members of the group are immune. Why does herd immunity occur?

What percentage of a population must be immune It happens because disease spreads from one person for herd immunity to operate? This percentage varies to another in any community. Once a certain proportion from disease to disease. A B Fig. B Number of cases observed as a result of herd immunity. Modified from American Academy of Pediatrics News. Copyright From Stickle G. Observed and expected poliomyelitis in the United States, — With transmission in the community has been interrupted.

A total of measles those who received the vaccine. The differ- theme parks between December 17 and 20, , the ence between the two curves represents the effect of suspected source of exposure. Of the secondary cases, herd immunity from the vaccine. From to , an average of 24, cases of paralytic poliomyelitis occurred in the United The incubation period is defined as the interval from States each year.

Two types of vaccine are available. If you become who are vaccinated but also others in the community infected today, the disease with which you are infected through secondary immunity, produced when the vac- may not develop for a number of days or weeks. During cinated individual spreads the active vaccine virus to this time, the incubation period, you feel completely contacts. In effect, the contacts are immunized by the well and show no signs of the disease. If enough Why does disease not develop immediately at the people in the community are protected in this way, the time of infection?

What accounts for the incubation chain of transmission is interrupted. However, even period? It may reflect the time needed for the organism inactivated poliovirus vaccine IPV , which does not to replicate sufficiently until it reaches the critical mass produce secondary immunity does not spread the virus needed for clinical disease to result.

It probably also to susceptibles , can produce herd immunity if enough relates to the site in the body at which the organism of the population is immunized. The dose of the infectious agent received at the time Therefore isolating such a person at the point at which of infection may also influence the length of the incuba- he or she becomes clinically ill will not necessarily be tion period.

With a large dose, the incubation period effective. On the other hand, isolation can be very may be shorter. In September , health officials in Saudi The incubation period is also of historical interest Arabia first reported a severe acute respiratory illness because it is related to what may have been the only with symptoms of fever, cough, and shortness of breath.

It was hoped that close contact, with health care personnel at higher risk this intervention would protect the community. In , of infection if universal precautions were not adhered in the Italian seaport of Ragusa, travelers were detained to.

All MERS-CoV cases that have been identified had in an isolated area for 30 days trentini giorni after a positive history of someone living in or traveling to arrival to see whether infection developed. This period countries in or near the Arabian Peninsula. Another was found to be insufficient, and the period of detention outbreak of MERS-CoV occurred in the Republic of was lengthened to 40 days quarante giorni. This is Korea in and was also linked to a returning traveler the origin of the word quarantine.

When a person is Fig. An important problem arises before 5, Note that, unlike the epidemic curve for the person becomes clinically ill—that is, during the common vehicle epidemics, the curve for person-to- incubation period.

If we knew when he or she became person spread is multimodal. An outbreak of MERS- infected and also knew the general length of the incuba- CoV in the Republic of Korea was seen in but tion period for the disease, we would want to isolate was rather contained, whereas the epidemic remains the infected person during this period and perhaps a active in Saudi Arabia.

A major contributor to the Korean few days extra to be especially cautious to prevent control of the epidemic was probably the strong infection transmission of the disease to others. In most situations, control measures implemented early on for diagnosing however, we do not know that a person has been and isolating probable MERS-CoV cases and for reducing infected, and we may not know until signs of clinical interpersonal contacts of travelers with a history of disease become manifest.

In addition, we may not know travel to highly affected areas. Different diseases have different incubation periods. This leads to an important question: Is it worthwhile A precise incubation period does not exist for a given to quarantine—isolate—a patient, such as a child with disease; rather, a range of incubation periods is char- chickenpox?

The problem is that, during at least part acteristic of that disease. In general the of clinical illness, he or she can transmit the disease length of the incubation period is characteristic of the to others. Thus we have people who are not yet infective organism. Thus, even when their disease. Onset date estimated if not available. World Health Organization.

Accessed May 14, New York: Plenum; For example, mesothelioma Fig. The incubation period for in Wales in Each bar represents the number noninfectious diseases is often referred to as the latency of cases of disease developing at a certain point in period. Incubation period, severity of disease, and infecting dose: evidence from a Salmonella outbreak. Am J Epidemiol. If we draw single-exposure, common-vehicle epidemic.

In fact, a line connecting the tops of the bars, it is called the this pattern is the classic epidemic curve for a single- epidemic curve, which is defined as the distribution of exposure common-vehicle outbreak Fig. The the times of onset of the disease. In a single-exposure, reason for this configuration is not known, but it has common-vehicle epidemic, the epidemic curve represents an interesting property: if the curve is plotted against the distribution of the incubation periods.

This should the logarithm of time rather than against time itself, be intuitively apparent: if the infection took place at the curve becomes a normal curve, which has useful one point in time, the interval from that point to the statistical properties see Fig. If plotted on onset of each case is the incubation period in that log-normal graph paper, we obtain a straight line, and person. The three critical variables in investigating an clusters among first-degree relatives of an index case outbreak or epidemic are as follows: heritability or clustering within families , which may 1.

When did the exposure take place? When did the disease begin? What was the incubation period for the disease? If we know any two of these, we can calculate the Exploring Occurrence of Disease third.

The concepts outlined in this chapter form the basis for exploring the occurrence of disease. When a disease Attack Rate appears to have occurred at more than an endemic An attack rate is defined as: usual level and we wish to investigate its occurrence, we ask: Number of people at risk in whom Who was attacked by the disease?

Total number of people at risk Where did the cases arise? It is well known that disease risk is affected by all The attack rate is useful for comparing the risk of of these factors. The attack rate can be specific for a given exposure.

For example, WHO the attack rate in people who ate a certain food is called The characteristics of the human host are clearly related a food-specific attack rate. It is calculated by: to disease risk. Factors such as sex, age, and race as well as behavioral risk factors e. Because women are more after an exposure most cases develop, the time period likely to be asymptomatic, the disease in women has is implicit in the attack rate.

Rates had been leveling A person who acquires the disease from that exposure off in both men and women over the past few decades, e. Such increases a primary case is called a secondary case.

The second- in rates among men could be either attributed to ary attack rate is therefore defined as the attack rate increased transmission or increased case ascertain- in susceptible people who were not exposed to the ment e. It is a good measure of person-to-person spread with men.

In , the rate was 1. The in noninfectious diseases when family members are number of cases in was the highest reported since examined to determine the extent to which a disease Rate per , population Men Women Total.

From Centers for 50 Disease Control and Prevention. Sexually Transmitted Disease Surveillance Accessed May 8, From Centers for Disease Control and Prevention.

Accessed June 13, Some of this increase may result from 2. Although the highest rate of pertussis was in improved diagnostics as well as recognition and report- infants less than 6 months of age 99 per , ing of cases. Approximately half of reported Although incidence rates showed two more peaks in pertussis cases in and occurred in to and , they subsequently declined until Of note, infants aged less than 1 year, who are at the Although the specific cause of this phenomenon is greatest risk for death, continue to have the highest unknown, it could result from a waning of protection reported rate of pertussis.

Summary of notifiable diseases, United States, Morb Mortal Wkly Rep. WHEN is most common during the summer months, and Certain diseases occur with a certain periodicity. For respiratory disease is most common during the winter example, aseptic meningitis peaks at consistent yearly months. The question of when is also addressed by rates Fig. Often, there is a seasonal pattern to examining trends in disease incidence over time. For the temporal variation.

The distribution of the disease closely parallels AIDS increased for many years, but it began to decline that of the deer tick vector. The basic cycle Disease is not randomly distributed in time or place. Mosquitoes become For example, Fig. When mosquitoes tion of Lyme disease in the United States in , with that bite both birds and humans become infected, they each dot representing one case of Lyme disease.

There pose a threat to people. Most human infections are is a clear clustering of cases along the Northeast coast, subclinical, but approximately 1 of infections in in the north-central part of the country, and in the recent years has resulted in meningitis or encephalitis.

Pacific Coast region. The states in which established The risk of neurologic disease is significantly increased enzootic cycles of Borrelia burgdorferi, the causative in people older than 50 years of age. The presence of a dot in a state does not necessarily mean that Lyme disease was acquired in that state. People travel between states, and the place of residence is sometimes different from the place where the patient became infected.

The case-fatality rate, or the from to Much remains to Advancing age is a major risk factor for death from be learned about this disease to facilitate treatment, WNV, with one study reporting death nine times as prevention, and control. Treatment is supportive, and prevention is largely Outbreak Investigation addressed through mosquito control and the use of insect repellents and bed nets.

Tracking the distribution The characteristics just discussed are the central issues of the disease depends on surveillance for human cases in virtually all outbreak investigations. The steps for and on monitoring birds and animals for the disease investigating an outbreak generally follow this pattern and deaths from the disease. Surveillance is discussed Box 2. Incidence per , 0. Number of cases 4, 3, 3, 2, 2, 1, Fig.

Week of onset. BOX 2. Examine the distribution of cases by the following: i. Time b. Look for combinations interactions of relevant Important considerations in investigating an acute variables outbreak of infectious diseases include determining that an 4. Develop hypotheses based on the following: outbreak has in fact occurred and defining the extent of the a.

Existing knowledge if any of the disease population at risk, determining the measure of spread and b. Analogy to diseases of known etiology reservoir, and characterizing the agent. Findings from investigation of the outbreak Steps commonly used are listed below, but depending on 5.

Test hypotheses the outbreak, the exact order may differ. Further analyze existing data case-control studies 1. Define the outbreak and validate the existence of an b. Refine hypotheses and collect additional data that outbreak may be needed a.

Recommend control measures 1 Clinical features: Is the disease known? Control of current outbreak 2 What are its serologic or cultural aspects? Prevention of future similar outbreaks 3 Are the causes partially understood? Prepare a written report of the investigation and the b. Communicate findings to those involved in policy c. Determine whether the observed number of cases development and implementation and to the public clearly exceeds the expected number d.

Calculate the attack rates. Based on cross-tabulation. This is illustrated by an outbreak of a second questionnaire, food-specific attack rates for food-borne streptococcal disease in a Florida jail items that were served to randomly selected inmates reported some years ago by the CDC.

On a questionnaire administered to Table 2. Outbreak of foodborne streptococcal disease. If the PDF link is not responding, kindly inform us through comment section. We will fixed it soon. We highly encourage our visitors to purch ase orig inal books from the respected publishers. Atlas Of Anatomy, 4th Maternal-neonatal Nursing Made Incredibly Small Cell Carcinomas: Causes, Author : G.

Alan Dever File Size : Ethics and Epidemiology Steven S. Coughlin — in Law. Author : Steven S. Coughlin File Size : Encyclopedia of Epidemiologic Methods Mitchell H. Gail — in Medical.