Phm570 Infectious Diseases Epidemiology Answers

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• Subject Code : PHM570
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• Subject Name : Epidemiology

Epidemiology and Control of Communicable Disease - Section 1

Ans1.1 (a):

Ans 1.1(b): The first step for the invasiveness of the disease is colonization of the microbe on the body surface. The mechanism of colonization involves attachment of the microbe to epithelial cells using bacterial pili. This interaction between the bacterial cells and the epithelial cells the prerequisite for invasive disease destruction. This happens via changes in the endothelial cells which is monolayer system and also this causes changes and also the in the tissue organization as well as in the intercellular spacing, causing the bacteria to invade inside the host cells.

 This occurs through small openings created in the intercellular spaces of the host cells. This changed structure of the endothelial cells surface is dependent upon two major mechanisms involving l aggregation of bacterial colonies on body surface and then subsequent signaling to endothelial cells which further lead to the formation of microvilli that surround the bacterial colony. This is dependent on both bacterial aggregation and signaling to the endothelial cells(Dani A. , 2014) that lead to the formation of microvilli surrounding the colony, protecting it from the flow.

Also the invasion is possible only if the bacterial strain resists itself from external stress and strains Therefore ultimate colonization can lead to invasive disease spread if it is resistant to external stress. Another major requirement for colonization to proceed to invasion is the presence of minor pilin PilX (Mehndiratta et al. , 2014)which help to strengthen the bacterial interactions and formation of large bacterial colonies leads to invasion.

Ans1.2 (a) Source of infection is infected needles and reservoir are the type 4 drug users i.e the carriers who carry the disease and transmit while sharing needles.

Ans1.2 (b): Immunogenicity affects transmission as immunogenicity refers to immune response generated by an organism against a vaccine or weakened antigen. Also as the humoral response is initiated it affects transmission patterns of the disease. This happens using the innate immunity and acquired immunity in response generated due to antigen sometimes unwanted immunogenicity (Ali, Chang, Johnson and Morris, 2018) i.e. unwanted response of the body to a vaccine or other antigen can worsen the condition and escalate the transmission patterns of the disease.

Immunity to some infectious agents is generated due to antibodies generated in response to antigen which follows carriage and infection i.e. leading to transmission.

Epidemiology and Control of Communicable Disease - Section 2

Ans2.1 a: The age of cases of paralytic polio in an endemic area is an important consideration as far environmental conditions and other sanitation measures are concerned. This is because paralytic polio worsens with age and the immunoglobins decrease to a significantly low level, also vaccines don’t respond much in older people. The environmental conditions including healthcare facilities and most important sanitation and sewage is important for proper waste disposal and if faecal matter of infected individuals is lying in open it will automatically affect the aged people of the endemic area first than effecting the young adults. Also immunity decreases with age so they are more susceptible to infectious diseases if environmental conditions are not appropriate.

Ans 2.1 b: The clinical: subclinical ratio of the disease is influenced by improved sanitation and environmental conditions as the disease is of low pathogenicity except elder aged individuals. The improved sanitation and environmental conditions reduce the ratio of disease as the spread and transmission patterns are cut off and no spread occurs due to proper disposal of infected faecal matter and also 1:20 proportion of the disease will further decrease and also there will be less of subclinical cases when environmental conditions improve.

Epidemiology and Control of Communicable Disease - Section 3

Ans 3(a) Sensitivity= true positive ÷ (true positive + number of false negative)

Sensitivity for test A =38÷42=0.904

Sensitivity for test B=29÷42=0.6904

Specificity =true negative÷ (true negative + false positive)

Specificity for test A=11990÷12103=0.9906

Specificity for test B=11989÷12103=0.998

Positive Predictive Value = number of true positives / number of true positives + number of false positives

PPV for test A=38÷ (38+113)

=0.251

PPV for test B=29÷ (29+114) = 0.202

Negative Predictive Value = number of true negatives / number of true negatives + number of false negatives

NPV for test A= 11990÷ (11990+4)

=0.9996

NPV for test B=11989÷ (11989+13) =0.9989

Ans3(b): The PPV is low in both tests as in both tests there is good sensitivity and specificity but low PPV as the likelihood of the disease is low and also many of the positive results from this testing procedure are false positives

Ans3(c): Test A is preferred as it has higher sensitivity.

Epidemiology and Control of Communicable Disease - Section 4

Ans 4(a): French onion soup

Odd ratio= (8÷51) ÷ (15÷45)= 0.47

Baked ham

Odd ratio= (21÷37) ÷ (18÷.42)=21.32

Parsley sauce

Odd ratio= (18÷40) ÷(15÷45)

=1.35

Odd ratio

(5÷54) ÷ (8÷52)=0.6

Creamed potato

Odd ratio= (23÷35) ÷ (23÷35) =1

Turnips and cabbage

Odd ratio=(30÷29) ÷(21÷38)

=1.87

Chicken curry

Odd ratio=(15÷44) ÷(7÷53)

=2.58

Sandwiches

Odd ratio=(6÷53) ÷(3÷56)

=2.11

Danish pastries

Odd ratio=(1÷58) ÷ (6÷53)

=0.15

Chocolate mousse cake

Odd ratio= (42÷16) ÷ (5÷53)

=27.83

Ice cream

Odd ratio= (10÷48) ÷(16÷43)

=0.56

Scones

Odd ratio=(1÷58) ÷(4÷56)

=0.56

Ans 4(b): The food item that most likely caused the outbreak was Chocolate mousse cake.

Ans4(c): The most likely chain of infection that would have resulted in Salmonella being transmitted from its reservoir to a susceptible host in this scenario is because of the cycle of conditions that make the transmission constant and does not allow for the chain of transmission to break

The chain of infection is a link between various elements which in this case is the transmission of salmonella through various foods and their consumption by several consumers.

All if one of the factors is removed, the chain of transmission is broken and spread of infection of infection stops. From reservoir to susceptible host the transmission pattern occurred through food served in the cafeteria and also the carrier for the disease is the food but many of the patients were asymptomatic .Then the escape of microbes from the food i.e. reservoir and and further release into the surroundings. After the release and escape, it is important for the microbe to find a certain carrier for the microbe as it needs a vector for its transmission and further mode of transmission to the susceptible case .This transmission occurs through the control host who themselves only carry the pathogenic microbe (Parikh et al., 2008) and themselves don’t get infected by the pathogen but transfer to the susceptible host.

Epidemiology and Control of Communicable Disease - Section 5

Ans5 (a): The majority of the population comprised of 14 and 40 years i.e the working adult force rather than a hub of senior citizens which is unproductive and retired .

The screening process was carried out for a long span of time and the cases per 100000 citizens escalated for gonorrhoea in a time span of 10 years i.e from from 1,250/100,000 population to 2360 /100,000 population.

The major reasons for the increased prevalence of gonorrhea among adolescents are :

• The major reason is the barrier to accessing STD prevention (Parikh et al., 2008) services and also increased levels of poverty and lack of proper transportation

(Barreto, 2006)Also the waiting times for the patients increased due to increased population and an embarrassment related to STD detection and society’s reaction Also there are increased concerns about concerns about confidentiality of the couple.

• Another reason for this substantial rise is the casual mindset of youngsters and preference to unprotected sexual practices and avoiding the use of condoms even in the vulnerable groups of the society.

ANS5(b): The host-adapted human pathogen Neisseria gonorrhoeae is the causative agent of gonorrhea. Gonorrhea is a sexually transmitted disease (Piszczek, St. Jean and Khaliq, 2015) in which the bacteria infect the protective layer of human genital organs.

 It occurs both in men and women, in women it occurs in the opening of the uterus by to penetrating the lining of the endocervix and in men it invades the inner lining of testicles causing pain and swelling.

1. gonorrhoeae breaks the internal tissue connections and sheds the cell lining by opening the intercellular spaces. And it lives in an immunosuppressive environment (Raad, 1997). A great damage is caused by the activation of innate immune responses where the bacteria colonize. In addition to this N. meningitides(Morris SK. ,2018 )can survive dehydration, and also survive outside the host body for longer spans of time and spread through respiratory droplet transmission.

ANS 5 (c): Most STI control guidelines recommend immediate anti-biotic treatment of high risk or symptomatic people for chlamydia and gonorrhoea, without waiting for confirmatory diagnostic tests. This is an important step towards the disease prevention by breaking the chain of transmission and by also weakening the bacterial core (Piszczek, St. Jean and Khaliq, 2015) and the antibiotics act upon those microbes and disrupt their invasion and prevent them from spreading in the whole body. Antibiotics prevents their exponential growth and doesnot allow the infection to spread to other parts of body, which if spread can be transmitted by casual contact through mucosal and oral lining droplets.

 Ans 5(d): An epidemiological characteristic of gonorrhoea is that it is asymptomatic in 80% of women and 10-15% of men test sensitivity will affect the sensitivity of gonorrhoea surveillance as sensitivity of the test helps to correctly identify those with the disease i.e. true positive rate whereas the asymptomatic cases will affect the test sensitivity as it will change the number of true positives if testing of the individuals is done only on the basis of physical symptoms. Also if testing is done in all patients then also the test sensitivity is low in asymptomatic patients

Ans5(e) : The implications about the epidemiological characteristic of the notification rates in both men and women in general and in this community clearly shows that the notification rates are much higher in women than men(Hachem R, et al. ,1997) in all the sexually transmitted infections. The cause for this might be unprotected sex due to ignorance of proper protection use by male partner. Also other implication is the sensitivity of the tests might be higher for women than men. Sometimes some tests are more sensitive towards women surveillance due to physiological and epidemiological characteristics thus sensitivity of tests changes and causes a huge difference in notification rate.

Epidemiology and Control of Communicable Disease - Section 6

Ans 6(a) The communicable disease is AIDS which is a Sexually transmitted disease and is communicable. It has high prevalence so sensitive case definition will help in detecting a lot of cases by contact tracing (Carmo , 2006) of sexual partners and check if they have the disease and are they potential carriers of the disease or if they donot have the disease and also check for asymptomatic cases.

Ans 6(b) Chickenpox is a communicable disease for which a very specific case definition should be used as it is symptomatic in all cases and the tests will to include only persons who truly have the disease under investigation but some other cases can be missed too as no lesions are observed on body.

References for Infectious Diseases Epidemiology

Ali, M., Chang, B., Johnson, K. and Morris, S., 2018. Incidence and aetiology of bacterial meningitis among children aged 1–59 months in South Asia: systematic review and meta-analysis. Vaccine, 36(39), pp.5846-5857..

Barreto, M., 2006. Infectious diseases epidemiology. Journal of Epidemiology & Community Health, 60(3), pp.192-195.

Dani A. (2014). Colonization and infection. Central European journal of urology, 67(1), 86–87.

Daniel TM, Robbins FC(1997). A history of poliomyelitis. Polio. Rochester, New York: University of Rochester Press;:5–22.

Mehndiratta, M., Mehndiratta, P. and Pande, R., 2014. Poliomyelitis. The Neurohospitalist, 4(4), pp.223-229.

Parikh, R., Mathai, A., Parikh, S., Chandra Sekhar, G. and Thomas, R., 2008. Understanding and using sensitivity, specificity and predictive values. Indian Journal of Ophthalmology, 56(1), p.45.

Piszczek, J., St. Jean, R. and Khaliq, Y., 2015. Gonorrhea. Canadian Pharmacists Journal / Revue des Pharmaciens du Canada, 148(2), pp.82-89.

Raad, I., 1997. Central Venous Catheters Coated with Minocycline and Rifampin for the Prevention of Catheter-Related Colonization and Bloodstream Infections. Annals of Internal Medicine, 127(4), p.267.

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