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Primary and Secondary Syphilis in North Carolina, 1980-2003
Maps Showing Progress toward Elimination

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HIV/STD Prevention and Care Branch

Syphilis rates, like those for other sexually transmitted diseases, have varied over time in North Carolina based on several factors. Undiagnosed and untreated cases can result in continued transmission of infection and subsequent increases in disease rates. One important factor to consider is that resources dedicated to case-finding and follow-up have decreased from the 1980 to the 1990s. Disease rates can also be impacted by disease patterns in surrounding states. Additionally, disease rates can fluctuate with changes in reporting patterns by health care providers. Because of its high syphilis morbidity, North Carolina is currently part of the National Syphilis Elimination Project.

The target for Healthy People 2010 Objective 25-3, Eliminate Sustained Domestic Transmission of Primary and Secondary Syphilis is 0.2 case per 100,000 population (2 cases per million). A baseline of 3.2 new cases per 100,000 in 1997 was used to help set the target for this objective.

The animated maps showing the incidence of syphilis in North Carolina over a twenty-year period are based on the concept of moving averages. Moving averages have the effect of "smoothing" random fluctuations in annual incidence rates due to small numbers of cases and small county populations generating them. They are useful for showing general trends of rates over a period of time.

The moving average rates for the animated map were calculated by summing the number of cases from the current year, the two previous years, and the next two years. The same process was used for state and individual county populations. The case sum was divided by the population sum and then multiplied by 100,000 to yield a five-year average incidence rate per 100,000 population. For more information about rates and their calculation please refer to the glossary. The results of these calculations are shown in the accompanying table. These rates are also depicted as part of the dynamic legend in the animated map. All rates for the maximum county column are based on twenty or more cases.

The rate classification scheme shown in the time series maps is based on equal numbers of counties in each of the four rate classes at the initial time period, labeled 1982. The values that demarcate the boundary between any two of the classes are held constant throughout the progression of maps. Over time, one can see that individual rate classes will shrink or expand with respect to the number of counties that they contain.

1. Division of Sexually Transmitted Disease Prevention. Sexually Transmitted Disease Surveillance Report, 2002. Department of Health and Human Services, Atlanta: Centers for Disease Control and Prevention (CDC), August 2003.

2. NC Division of Public Health, HIV/STD Prevention and Care Branch

3. Five-year moving average rate calculated by sum of 5-years of P&S Syphilis cases ÷ sum of 5 years of total population × 100,000

4. The highest individual county 5-year average rate for the year - these rates are based on 20 or more cases

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Page Last Updated Friday March 09 2012