Public Health Prevention Strategies For Salmonellosis At Cockatoo Rest Hospital

Incidence Rates of Salmonellosis in Cockatoo Rest Hospital

Discuss about the Infectious Disease Report For Cockatoo Rest for Incidence Rate.

Cockatoo Rest hospital was facing increasingly staff shortage especially nursing staff. This was linked to increased hospitalization due to infectious by three main conditions; salmonellosis, Ross River virus and Influenza. The hospital and the local authorities, realizing the difficulty attracting and retaining health professionals in a rural area, saw the need to devise preventive public health strategies to reduce the number of hospitalizations and in turn reduce the staff shortage.

The current paper is a report on the public health prevention strategy for salmonellosis. The paper will discuss the incidence rates of salmonellosis in Cockatoo Rest compared with the rest of Australia. The 5-year cumulative incidence and the annual incidence rates will be calculated from health data for Cockatoo Rest. The two incidence rates will be compared and contrasted. The modes of transmission and epidemiologic (person, place, and agent) factors underpinning this transmission will be analyzed. Finally, proposed public health strategies targeting select transmission factors will be posed with reduction of transmission and incidence rate in mind.

The following table shows epidemiologic health data for salmonellosis in Cockatoo Rest.

Incidence is a measure of disease frequency that measures the rate at which new infections are happening in a population at risk during a specified period of time (Webb, Bain and Page 2016, p.36). In the above health data, the assumption that the population at the beginning of each year is the population at risk and that no one had the disease at that time will be applied to the calculation of disease incidence.

It is the number of new salmonellosis cases occurring in the population per person-time at risk also termed the incidence density (Webb, Bain and Page 2016, p.36).

Incidence rate=   the number of new cases in a defined time period × 100,000 The total population at risk

From the formula, the annual incidence rates are as follows:

2011 = 3/4553 × 100,000 = 65 per 100,000

2012 = 2/4572 × 100,000 = 43 per 100,000

2013 = 3/4637 × 100,000 = 64 per 100,000

2014 = 8/4591 × 100,000 = 174 per 100,000

2015 = 4/4688 × 100,000 = 85 per 100,000

The cumulative incidence also known as incidence risk is the proportion of a population at risk of developing the disease who actually develop the disease during a specified period of time (Webb, Bain and Page 2016, p.39). It represents the average risk or the probability that an individual at risk in a certain population will develop the disease (Webb, Bain and Page 2016, p.39).

Modes of Transmission and Epidemiologic Factors of Salmonellosis

Cumulative incidence is given as:

The number of new cases in a defined time period

The total population at risk at the start of the study period

It is expressed as a probability (0-1) or percentage (0-100%).

From the above formula the cumulative incidence of salmonellosis in Cockatoo Rest is:

 20/4553 × 100 = 0.44 % over five years. 

The numerator for both is the same in that is it the number of individuals who developed salmonellosis during the observation period. However, the denominators are different. For cumulative incidence, it is the total number of the individuals at risk being followed in this case at the beginning of the five-year period. For incidence rate, it is the total population at risk in time-person years (Webb, Bain and Page 2016, p.40). The incidence rate is a more accurate measure of the rate at which salmonellosis infections occur annually for example in 2011 it was 65 per 100,000, reduced to 43 per 100,000 in 2012, increased to 64 per 100,000 in 2013, then to 174 per 100,000 and finally 85 per 100,000 in 2015. Cumulative incidence, on the other hand, is a proportion and denotes the probability of developing salmonellosis for the population in the five-year period. The percentage probability was 0.44% for the population followed up for five years.

Since the population is dynamic and the follow-up period is long (five years), annual incidence rates are more advantageous than cumulative incidence (Vandenbroucke and Pearce 2012). Cumulative incidence is more appropriate for closed populations with little additions or withdrawals (Vandenbroucke and Pearce 2012).

The incidence rate of salmonella in Australia has been increasing over the past few years (Wilson, Kennedy and Moffatt 2018). According to OzFoodNet Working Group (2015), surveillance of salmonellosis outbreaks reports 12,271 cases of salmonellosis which translated to an incidence rate of 54.3 cases per 100,000. Data for Cockatoo Rest in 2011 showed the incidence rate of salmonellosis was 65 per 100,000. Compared to Australian figures, the incidence rate is higher in Cockatoo Rest. However, both Cockatoo Rest and Australia are experiencing a rise in the incidence rates of salmonellosis (Ford et al. 2016).

The epidemiologic triad of agent factors, host factors, and environmental and social factors will be discussed in reference to salmonellosis. 

Salmonellosis is caused by Salmonella typhi, a bacterium from the family Enterobacteriaceae. It is a gram-negative, facultative aerobic, non-spore forming bacteria (Ryan and Ray 2014, p.362). Humans are the only known hosts of this bacterium. Infection by salmonella typhi renders one either a case or a carrier (Ryan and Ray 2014, p.362). Cases are individuals with the disease and continue to shed bacilli in stool or urine and have the bacilli circulating in the bloodstream. Carriers, on the other hand, excrete bacilli without having clinical evidence of the disease process since they have cleared the infection. This is possible as the bacterium can survive in the gallbladder without causing disease in the carrier (Ryan and Ray 2014, p.362). An example is the famous case of Mary Mallon, a cook in New York in the 1900s, famously nicknamed ‘typhoid Mary’ for being a carrier and infecting close to 1300 cases in her lifetime (Marineli et al. 2013)

Proposed Public Health Strategies for Salmonellosis Prevention

The primary sources of infection are feces and the urine of the disease cases and carriers (NSW Government, 2018). The secondary sources of infection include contaminated food, contaminated water, fingers or flies. The bacteria invade the payer’s patches of the small intestine to initiate infection. It then invades the bloodstream and travels to the liver and spleen and re-infects the lymphoid tissues to bring about the clinical symptoms (Ryan and Ray 2014, p.363).

Salmonellosis infection occurs at any age but is more predominant in the young. There is a sex predominance as it tends to affect males more than females (Shetty 2009). However, carrier rates are more in females than males. Immunity to this infection is either through infection or immunization (Shetty 2009). This raises the concept of herd immunity whereby the population can be immune to the disease if significant members of itself are immune to it mostly through immunization (Shetty 2009).

Typhoid is termed a sanitation disease and is generally a disease due to poor sanitation and hygiene (Baaten et al. 2010). This is the reason it might be more prevalent in poor social settings and poor countries have higher incidence rates. Poverty states such as lack of sanitation facilities, unsafe drinking water or practices such as open defecation are associated with increased cases (Ahmad and Akil 2017). The incidence is usually same throughout the year but rises during the rainy season and with increased fly populations. (NSW Government 2018). Some occupations such as food handlers and cooks are in a greater position to spread the disease (Chousalkar et al. 2017) 

Salmonellosis is a food-borne disease transmitted mostly by the fecal-oral route (Levantesi et al. 2012). This includes directly through hands soiled with feces or urine of cases or carriers or indirectly by ingestion of contaminated water/ice, milk/ice cream, food, or through flies (Ryan and Ray 2014, p.362).

A study was conducted by Bhunia et al. (2009) in response to a typhoid fever outbreak in a slum in south Dumdum municipality in West Bengal, India in 2007. The study aimed to find evidence of foodborne and waterborne transmission of typhoid fever. The study design was an analytical case-control study. The outcome was defined as fever for more than one week among the residents. The cases were sought from health facilities and blood samples collected to identify confirm the disease. The results were matched with neighborhood-matched controls.

The results of the study identified 103 cases with isolation of Salmonella typhi from one in four of the blood samples. The suspected cases were mapped and they clustered around three public water taps. Among 65 of the cases, eating milk products from a shop and drinking the piped water led to infection. The shop handler was followed and discovered to have suffered typhoid earlier in the year. The conclusion from the study indicated that initially, food contamination led to water contamination proving typhoid to be a food-borne and water-borne disease.

Comparison of Incidence Rates in Cockatoo Rest Hospital and Australia

According to Frieden (2014), a good public health strategy should have six elements to be successful. They include; 1) Innovation that guides the development of the action plan. 2) A good package of interventions that are of high priority and guided by evidence. 3) Proper management of the project through monitoring, evaluation and improvement of key areas as needed. 4) Intersectoral collaboration with the involvement of both public and private sector. 5) Communication with stakeholders including healthcare professionals, the community, the civil society and major decision makers in order to effectively impact or behavior change. 6) Commitment by the government and authorities to obtain and supply resources to support the project.

The high priority areas that are recommended for the eradication of salmonella will be aimed at the host factors and the environment or community (NSW Government 2018). The host factors that are modifiable and could be targeted in the intervention include host immunity. The environmental factors that are modifiable and could be targeted include hygiene and sanitation, unsafe drinking water, defecation and urination practices, food handling practices and social economic status (Baaten et al. 2010).

Vaccination against typhoid fever is a valid strategy at the level of the susceptible host (Centre for Disease Control 2012). The salmonella typhi antigenic structure is such that it has two sets of antigens that can be targeted. It has somatic or O antigens and flagellar or H antigens (Ryan and Ray 2014, p.363). Vaccines against these antigens have been formulated and would help reduce the incidence of typhoid fever. Examples include injectable Typhoid vaccine (TYPHIM-Vi, TYPHIVAX) which is given as a single subcutaneous or intramuscular shot with an efficacy of 64 to 72% (CDC 2012). It is recommended and safe to use in children over the age of two years. A live oral vaccine is also available (TYPHORAL) (CDC 2012). It is taken with milk before food and is suitable for children over six years. It offers immunity after two weeks and a booster is needed after three years.

The benefits of vaccination against typhoid in this setting include the acquisition of herd immunity. It is immunity conferred to an individual against an infection due to large numbers of the population being immune to the infection (Rashid, Khandaker, and Booy 2012). This strategy is also feasible in this setting due to the small population making it relatively cheap to implement.

The intervention aimed at the community and the environment should be water sanitation. Public health strategy aimed at water and sanitation should include the following agenda: sources of safe drinking water, provision of safe drinking water, avoiding contamination of water and health education on maintaining the same (NSW Government, 2018). The community should be directed to safer drinking safer including rainwater, piped water, and uncontaminated protected wells. They should avoid surface running water which is more prone to contamination. Treatment of drinking water is another strategy that will guarantee water safety. It could involve boiling, chlorination or industrial water treatment. Stakeholders in the public health project should ensure the provision of safe drinking water Health education is aimed at reinforcing behavior change concerning these recommendations. The community is educated on salmonella typhi transmission and the importance of sanitation, water safety, and food safety. Intervention such as handwashing using soap and clean water, methods of proper food handling and ways of treating drinking water can be introduced during this phase of intervention (NSW Government 2018).

Conclusion

Conclusion

Public health strategy to tackle the rising problem of salmonellosis is warranted as shown by the rising incidence rates of the disease in Cockatoo Rest. The annual incidence rates for the period between 2011 and 2015 was 65 per 100,000 in 2011,43 per 100,000 in 2012, 64 per 100,000 in 2013, 174 per 100,000 in 2014 and 85 per 100,000 in 2015. The cumulative incidence for the period of five years was 0.44%. Compared to Australian data, both showed rising incidence rates. However, incidence rates in Cockatoo Rest were higher.

Salmonellosis is a disease caused by the bacterium Salmonella typhi and is transmitted by the fecal-oral route. This is by ingestion of food or water contaminated by feces or urine from a case or carrier of the disease. It is a disease of poverty and poor sanitation.

Public health strategies should be aimed at the agent, host or environmental factors to be effective. The chosen public health strategy for the prevention of salmonellosis include vaccination, water sanitation, and health education. 

References 

Ahmad, H and Akil, L 2017, ‘Effects of Environment and Socioeconomics on Salmonella Infections’,Current Topics in Salmonella and Salmonellosis. InTech.

Baaten, G, Sonder, G, Van Der Loeff, M, Coutinho, R and Van Den Hoek, A 2010, ‘Fecal?orally transmitted diseases among travelers are decreasing due to better hygienic standards at travel destination’, Journal of travel medicine, 17(5), pp.322-328.

Bhunia, R, Hutin, Y, Ramakrishnan, R, Pal, N, Sen, T and Murhekar, M 2009, ‘A typhoid fever outbreak in a slum of South Dumdum municipality, West Bengal, India, 2007: evidence for foodborne and waterborne transmission’, BMC public health, 9(1), p.115.

Centre for Disease Control 2012. Typhoid vaccines. [online]. Available at https://www.cdc.gov/vaccines/hcp/vis/vis-statements/typhoid.html

Chousalkar, KK, Sexton, M, McWhorter, A, Hewson, K, Martin, G, Shadbolt, C and Goldsmith, P 2017, ‘Salmonella Typhimurium in the Australian egg industry: a multidisciplinary approach to addressing the public health challenge and future directions’, Critical reviews in food science and nutrition, 57(12), pp.2706-2711.

Ford, L, Glass, K, Veitch, M, Wardell, R, Polkinghorne, B, Dobbins, T, Lal, A and Kirk, M.D 2016, ‘Increasing Incidence of Salmonella in Australia, 2000-2013’, PloS one, 11(10), p.e0163989.

Frieden, T 2014, ‘Six Components Necessary for Effective Public Health Program Implementation’, American Journal of Public Health, 104(1), pp.17–22. https://doi.org/10.2105/AJPH.2013.301608

Levantesi, C,  Bonadonna, L, Briancesco, R, Grohmann, E, Toze, S and Tandoi, V 2012,’Salmonella in surface and drinking water: occurrence and water-mediated transmission’,Food Research International, 45(2), pp.587-602.

Marineli, F, Tsoucalas, G, Karamanou, M and Androutsos, G 2013, ‘Mary Mallon (1869-1938) and the history of typhoid fever’, Annals of Gastroenterology: Quarterly Publication of the Hellenic Society of Gastroenterology, 26(2), p.132.

NSW Government 2018, Salmonellosis fact sheet. Sydney: NSW Government

OzFoodNet Working Group 2015, ‘Monitoring the incidence and causes of diseases potentially transmitted by food in Australia: Annual report of the OzFoodNet network, 2011’, Communicable diseases intelligence quarterly report, 39(2), p.E236.

Rashid, H, Khandaker, G and Booy, R 2012, ‘Vaccination and herd immunity: what more do we know?’, Current opinion in infectious diseases, 25(3), pp.243-249.

Ryan, KJ and Ray, CG eds. 2014, ‘Sherri’s medical microbiology’, McGraw-Hill Education/Medical.

Shetty, N 2009, ‘Basic concepts of the epidemiology of infectious diseases’, Infectious Disease: Pathogenesis, Prevention and Case Studies, p.157.

Vandenbroucke, JP and Pearce, N 2012, ‘Incidence rates in dynamic populations’, International journal of epidemiology, 41(5), pp.1472-1479.

Webb, P, Bain, C and Page, A 2016, ‘Essential Epidemiology: an introduction for students and health professionals’, Cambridge University Press.

Wilson, HL, Kennedy, KJ and Moffatt, CR 2018, ‘Epidemiology of non?typhoid Salmonella infection in the Australian Capital Territory over a 10?year period’, Internal medicine journal, 48(3), pp.316-323.

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