General principles of Epidemiology




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As Gordis(2008, pg 9) shows, there were differences in the reported cases of gonorrhea in 2005. This was observed in a descriptive study on the state of the gonorrhea infection. There are reasons why there are differences in the number cases. Since the analysis shows that the numbers given are valid, then there are differences in the risk factors among the states or there would be problems in data collection.

According to Blackburn (2011), the numbers of gonorrhea cases that are reported in different US states do not reflect accurately the level of prevalence of the disease. This is commonly caused by problems in data collection. There are two factors that limit the accuracy of the data collected. First, some doctors do not screen patients routinely and secondly some hospitals fail to report all positive cases of gonorrhea to the Health Department as the law requires.

Linda (2005) shows that the method of data collection may limit the quality and accuracy of the data collected. Data collection methods in the study of the prevalence of gonorrhea include face-to-face interviews; document sources for instance reports from the state health department, self reports and computerized or on-line methods. The methods reveal significant variation in the number of gonorrhea infections. Self report is the most appropriate method of data collection in case of gonorrhea because through this method, a greater case assessment can be reached.

Gorgos (2011) illustrates that the target population in the study of gonorrhea should be the risk groups. For example, the prevalence of gonorrheain the 2005-2007 study among black women aged between 15-24 years attending family plan clinics in different US states revealed that the morbidity of gonorrhea was concentratedin this risk group.Factors such as location, age and gender of the target group determines accuracy of a study.


Blackburn, J. (2011). Territory’s STD rates among highest in U.S. United States, Washington: McClatchy – Tribune Information Services.

Gordis, Leon. Epidemiology,4thEd, pg 9.2008, USA

Gorgos L. (2011), GonorrhoeaPositivity among Women aged 15-24 Years In The USA, 2005-2007, Infectious Disease Bureau, New Mexico Department of Health USA

Linda M. Niccolai, PhD, Data Collection for Sexually Transmitted Disease Diagnoses:Annals of Epidemiology,Vol15, Iss3,Pg 236-242, March 2005



Gordis(2008, pg 14) explains that in studies done on two water companies along the Thames River in South London, the water company that moved its water intake upstream showed lover cholera morbidity compared to the company that retained its water intake downstream. Farr, the Registrar General in this area realized that areas that received water from a higher elevation above sea level registered less deaths from cholera, he thus instructed the registrar of each district to record the company that supplied water to each home where a person died of cholera.

In accordance to Piarroux(2011) when cholera epidemic was experienced in Haiti in October 2010, studies done using the regression model showed that the communities severely affected by cholera were those who lived along the coastal plane with a risk ratio of 4.91. This was caused by the contamination of the ArtiboniteRiver downstream from one of its tributaries from a military camp located at a higher altitude.

This shows that water at a lower altitude is more likely to be contaminated by bacteria because of gravitational downstream flow of germs from homes and plants in higher elevation above sea level.

Gordis, Leon. Epidemiology. 4thEd. pg14, 2008,USA

Piarroux R. (2011), Understanding the Cholera Epidemic, Haiti,US National Library of Medicine National Institutes of Health, USA.


Gordis (2008, pg 19) asserts that a variety of factors determine the degree to which people are susceptible to illnesses. These factors include immunological characteristics of an individual, nutritional status and his/her genetic makeup/ genotype.

According to Carapetis(1999) the highest prevalence of rheumatic fever ever published was among the Australia’s aboriginal people. Transmission and infection of group A streptococcal bacteria is common here due to poor nutrition and hygienic conditions, overcrowding and scabies infestation all being factors associated with this bacterium.Their genetic makeup also makes them susceptible to streptococcal infection that causes rheumatic fever. In addition there are no public health programs in these developing communities. In addition secondary prophylaxis regimens are not delivered in the communities hence no prevention of recurrences of rheumatic fever.

Gibofsky (2001)shows that in USA the incidence of acute rheumatic fever was only 2 to 14 cases per 100,000 because antibiotics for streptococcal bacteria are routinely used in this developed economy as compared to developing economies.

Allan Gibofsky, MD(2011), Epidemiology and Pathogenesis of Acute Rheumatic Fever, Rockefeller University, USA.

Carapetis, J. R.,& Currie, B. J. (1999). Mortality due to acute rheumatic fever and rheumatic heart disease in the northern territory: A preventable cause of death in aboriginal people.Australian and New Zealand Journal of Public Health, 23(2), 159-159-163.

Gordis, Leon. Epidemiology. 4thEd. pg 19, 2008, USA


According to Queensland Government (2009), the signs and symptoms that a swine flu infection shows resemblesthose of other influenza like illnesses. This means that it is difficult to determine whether the clinical manifestations in a patient are those of swine flu or seasonal influenza. This happens especially in the early days of infection unless patients are screened for antibodies as it happens during an outbreak.


Queensland Government, 2009, Human Swine Flu: Questions and Answers, Queensland Government, Viewed on 13/08/2011,


CIDRAP (2010) reported that it is not easy to come up with an estimation of the number of reported asymptomatic cases of influenza infection as the infection may show any symptoms. However one fourth of health care professionals in Atlanta were reported to have asymptomatic H1N1 in 2010 when the pandemic was in its early stages. It was found that 35 out of 140 of health workers (28.5%) tested positive of thevirus.


CIDRAP, 2010, ICEID NEWS SCAN: Thermal scanners, asymptomatic H1N1 in HCWs, pandemic vaccine wariness, dengue in Florida, food borne disease patterns, CIDRAP, Viewed on 12/08/2011,


Urban(2009)demonstrates that it is not possible to quarantine swine flu infected individuals because of its world wide spread. But because it is highly infectious, it must be controlled. Even if it is widely spread its contagious and deadly nature cannot allow us to stop containing the infection. Controlling it will prevent a catastrophe especially among pregnant women and children.

Urban, M. (2009).Sanitizers loaded, 5 campuses ready: Aware of their potential as hotbeds in a double-barrel influenza season, berks colleges plan to combat, contain this year’s seasonal and swine flu. United States, Washington: McClatchy – Tribune Information Services.


Jerry (2010) states that in typhoid fever, a common vehicle outbreak implies that the outbreak resulted from consumption of contaminated food or drinking water contaminated with the Salmonella species.

In the case presented here all people in the cruise ship who had consumed food in Papua New Guinea got the infection within 14 hours of their stay there. Therefore the cause must have resulted from acommon vehicle or a single exposure and not likely to be that of a prolonged person to person typhoid fever outbreak.

Jerry. B. (2010), Typhoid Fever, Medicine Net. Com, Viewed on 12/08/2011,




In this case the outbreak of typhoid fever was caused by consumption of contaminated food. Therefore herd immunity does not play any role because there was no prolonged person to person spread, the characteristic of herd immunity.


30 out of 35 people who ate at Burka’s (85.7%) developed typhoid fever and only 2 out of 20 people who ate at Joe’s (10%) developed the fever. Therefore the most likely source of the Salmonella typhiwas at the Burka’s.


Total number at risk (Ate) =70

Total number not at risk (Did not eat) =30

Total number who developed typhoid fever =42

Attack rate = total infections/total at risk = 42/70


The two patients in table 2 who ate at Joe’s must have got the contamination from contact with the travelers who ate at Burka’s because it is very unlikely that the source of the infection was from Joe’s.


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