[Zika virus and sexual transmission; when and for how long does one need to use a condom?] / Zikavirus en seksuele transmissie.

- More evidence has become available concerning the sexual transmission of Zika virus and viral shedding in semen, which has led to the expansion of international guidelines for prevention of sexual transmission; Dutch guidelines have not been altered.- Internationally, the use of condoms during sex or sexual abstinence is advised for the duration of the pregnancy. Furthermore, when actively trying to conceive one should use a condom for six months.- In the Dutch guidelines, men who have visited a Zika virus epidemic area are advised to use a condom for 2 months upon return, irrespective of their partner possibly being pregnant or their wish to conceive.- Based on reports to the World Health Organisation and patient reports, the serial interval between disease onsets of both sexual partners is 4-44 days (median: 15).- Zika virus RNA is often no longer detectable in semen 2-3 months after disease onset.- International guidelines are based on the maximum detection period of Zika virus RNA and on virus isolation. Dutch prevention guidelines, on the other hand, are based on the longest serial interval known for sexual transmission (44 days).- Detection of Zika virus RNA in semen does not give a definitive answer on contagiousness. Currently, following the Dutch prevention advice is the best option in order to prevent sexual transmission.

Waning population immunity prior to a large Q fever epidemic in the south of The Netherlands.

Historical survey data suggest that the seroprevalence of antibodies against Coxiella burnetii in the general population of The Netherlands decreased from more than 40% in 1983 to 2·4% in 2007, just before the start of the large 2007-2010 Q fever epidemic. To assess whether the sharp decline in seroprevalence was real, we performed a cross-sectional study using historical samples. We tested samples using a contemporary commercial indirect immunofluorescence assay. In plasma samples from the south of The Netherlands from 1987, we found an age- and sex-standardized seroprevalence of 14·4% (95% confidence interval 11·2-18·3). This was significantly lower than a 1983 estimate from the same area (62·5%), but significantly higher than 2008 (1·0%) and 2010 (2·3%) estimates from the same area. The study suggests that there was a steady and sharp decline in Q fever seroprevalence in the south of The Netherlands from 1987 to 2008. We assume that seroprevalence has decreased in other parts of The Netherlands as well and seroprevalence surveys in other European countries have shown a similar declining trend. Waning population immunity in The Netherlands may have contributed to the scale of the 2007-2010 Q fever epidemic. For a better understanding of the infection dynamics of Q fever, we advocate an international comparative study of the seroprevalence of C. burnetii.