5v contact closure SSR?
You can use a simple optoisolator if the current is &lt; 10uA and DC less than 50V. 

For example, a  TLP620(F). 







simulate this circuit &ndash; Schematic created using CircuitLab

R2 is probably not necessary, but if necessary it might help it switch faster. Chances are you only need R1 and the optoisolator. The circuit draws about 10mA without R2, and 15mA with R2. 

This circuit provides "galvanic isolation" so if there happens to be a few volts between the USB host and whatever you are connecting the "contact" to, nothing unfortunate will happen.