Module 3: Final Case Study

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Case Study: Instructions

 Try this case study individually.  We’ll discuss the answers in class.

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Answers to Final Case Study Question 1

1. You are the HIV surveillance officer for Inyo Province in the Mono Republic. Inyo Province currently conducts HIV sentinel surveillance at antenatal and STI clinics serving female sex workers. You are considering adding more sites to the province’s sentinel surveillance system.

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Answers to Final Case Study Question 1, continued

a. What must you consider when selecting sites for sentinel surveillance?

The selection of sites for HIV sentinel surveillance is a balance between including as much of the selected population as possible and logistical necessities. In order to ensure success, sentinel surveillance should be implemented in facilities with enough personnel and laboratory capacity to conduct a successful survey. Other factors to consider include, the populations being served by the site, whether blood samples are routinely collected at the site, the laboratory facilities available, the size of the client base, and the geographic diversity of sites.

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Answers to Final Case Study Question 1, continued

b. In Inyo Province, the estimated prevalence of HIV is 35% among female sex workers. What would be an adequate sample size to measure HIV prevalence within a margin or error of +/- 5%?

Using the following formula: N = 4zα2P (1-P) ÷W2 The calculation would look like this: N = [4 x (1.96)2 x 0.35 x (1 - 0.35)]

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(0.10)² N = 350 people Therefore you need 350 people in your sample in order to achieve the confidence interval that you want.

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Answers to Final Case Study Question 1, continued

c.

What method of HIV testing would be most appropriate in conducting sentinel surveillance of female sex workers attending STI clinics?

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Answers to Final Case Study Question 1, continued

c.

Unlinked anonymous testing or linked testing with informed consent. Unlinked anonymous testing may be appropriate in this situation as UAT relies on blood that is left over from specimens that are regularly collected for other purposes (such as syphilis testing). The major disadvantage of unlinked anonymous testing is that persons do not get their test results. Since such information may directly impact their health and risk of acquiring or transmitting HIV, unlinked anonymous testing should be done in settings where patients can be referred to voluntary counselling and HIV testing programmes. The benefit of unlinked surveys is that it minimizes participation bias. In settings where treatment is available or when the target population is not easily accessed in health settings, linked testing (confidential or anonymous) with informed consent is preferred as patients receive their tests results.

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Answers to Final Case Study Question 1, continued

d. Inyo Province conducts HIV surveillance at 20 sentinel sites. As the HIV surveillance officer for Inyo Province, you are charged with supervising the staff at all sentinel sites. How would you ensure that sentinel site staff are adequately trained and that surveillance is conducted in the same manner at all sentinel sites?

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Answers to Final Case Study Question 1, continued

d. To ensure that the surveillance process is smooth and effective, be sure that all staff undergo the necessary training. As the HIV surveillance officer in charge of supervising staff at all sentinel sites, you should monitor all aspects of sentinel surveillance, including: sampling, data and specimen collection and management and laboratory equipment. As it is impossible for you to be present to supervise at all facilities, you may delegate to other supervisors. These other supervisors may then delegate, if need be, to a supervisor at the facility level.

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Answers to Final Case Study Question 2

2. HIV surveillance at various sentinel sites between 1999 and 2005 found the following data:

HIV Prevalence at select sentinel site in Inyo Province, 1999-2005. Group Pregnant women Pregnant women STI patients Sex workers Tuberculosis patients Tuberculosis patients No. of sites

6 2 2 5 1 1

Area

urban rural urban urban urban rural

1999

32% 17% 52% 63% -

2001

30% 19% 57% 66% -

2003

23% 20% 54% 61% 73% 32%

2005

21% 22% 51% 55% 82% 36%

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Answers to Final Case Study Question 2, continued

a. What trends do you see? At which sites would you expect HIV prevalence to be the highest in 2006?

Among urban pregnant women HIV prevalence peaked in 1999 and decreased between 1999 and 2005. Among urban pregnant women, the greatest decrease was observed between 2001 and 2003. Rural pregnant women consistently had a lower mean prevalence compared to urban pregnant women. HIV prevalence among STI patients and sex workers peaked in 2001 and decreased thereafter. Among TB patients, the prevalence of HIV increased between 2003 and 2005 and was highest in TB patients in urban areas. In 2006, HIV prevalence will probably be highest among urban TB patients.

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b. What are the limitations of the above data? What are the limitations of sentinel surveillance?

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Answers to Final Case Study Question 2, continued

b.

Limitations of the above data include: No data on TB patients until 2003. Only two data points sero-surveillance in TB patients make it difficult to determine a trend for TB patients. The small number of site, particularly for TB and STI patients limits the ability to generalise findings from sentinel surveillance.

Limitations of sentinel surveillance data include: most sentinel surveillance is conducted among pregnant women attending ANCS and thus do not provide information about non-pregnant women or men. Additionally, because coverage of rural areas by the sentinel surveillance system in most countries in incomplete, the assumptions and validity of estimates derived from sentinel surveillance are often questionable.

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Questions, Process Check

 Do you have any questions on the information we just covered?

 Are you happy with how we worked on the final case study?  Do you want to try something different that will help the group?

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