Syphilis and Gonorrhoea: Portugal Trend and Seasonality

Cátia Dias, Rita Félix, Pedro Damião

Keywords: Syphilis; Gonorrhoea; Trend; Seasonality;

Infection with Treponema pallidum and Neisseria gonorrhoeae are a global problem. The World Health Organization estimates that, worldwide in 2016, there were 19.9 million cases of syphilis in adolescents and adults aged 15 to 49 years, and 6.3 million new cases. Gonorrhea was responsible for about 80.7 million infections in 2016, worldwide. Is difficult to establish the real number because of the lack of diagnostic capability and reporting systems in many parts of the world. In Portugal, these illnesses are included in the list of notifiable diseases, therefore it is important to assess the trend and temporal distribution of their notifications in order to
understand whether further measures are needed to reduce the number of new notifications.

Research questions:
The aim of this study is to assess the temporal evolution and distribution of gonorrhea and syphilis notifications in mainland Portugal, between 2015 and 2018.

Descriptive observational study of the ecological type, with data collected from PORDATA and the National Health Service’s Transparency Portal, processed and combined with the R (3.4.2) for the production of distribution graphs. A linear model for a short temporal series (January/2015- December/2018, monthly resolution) was created with a trend component and a seasonal component (the seasonal pattern was approximated by fourier terms).

There is a clear increase in the number of notifications between 2015 to 2018 in both illnesses (gonorrhea: trend coef. 1.1792, p<0.0001, syphilis: trend coef, 0.4797, p<0.0006). Contrary to syphilis, gonorrhea model shows a periodic component [coef fourier (df, 2)S2- 12=6.7334, p=0.0272]. Gonorrhea and Syphilis notifications were always higher in male population (female 11.5% and 26.2%, respectively).

Gonorrhea and syphilis are a major cause of morbidity among sexually-active individuals in Portugal (as worldwide), particularly in males, and these data revealed a need for intervention in this area.

Points for discussion:
Which are the temporal evolution and distribution of gonorrhea and syphilis?

How to improve the diagnosis of syphilis and gonorrhea?

How to decrease the syphilis and gonorrhea new cases?