It is important to note that regardless of the underlying targets, MHUs must not be viewed as permanent solutions, due to the limitations in numbers of services provided and high operating costs.  In other words, MHUs are not viable stand-alone units that should be viewed as a part of the country's health infrastructure.  MHUS are specifically to be used when there is no other option, and retired once the situation has stabilized. There are many other considerations which are important to be aware of when deciding how and when to use MHUs.  Du Mortier and Coninx highlight a few of these.