Hi Carol,
Ameda/Hollister's hygeinikits are closed systems, the piston motor of
the pump removed air from a silicone diaphragm at the top of the kit,
which contracts, forming negative pressure in the nipple tunnel/breast
shell.  Because of this diaphragm, no air from the pump contacts the
milk, and no milk can enter the tubing, and therefore no milk can enter
the motor.  The kit will not assemble tightly without the diaphragm,
preventing it from being used without the diaphragm.
        Medela kits use a silicone filter to capture viruses in the air that
passes through the kit.  It is still possible for milk to back up in to
the motor in this case.  The company states that their tests show that
viruses cannot pass their filter.  If milk is backed up into the motor,
it must be returned to Medela for cleaning to provide proper operation,
and to protect other users.
        This is how we can allow hospital pumps to be used by more than one
mother.
        Ameda's Purely Yours could safely be used by more than one mother,
because it uses the closed system hygeinikit, but it is not durable
enough to be passed around indefinately.  It is classified as a personal
pump, because it is made to be lightweight, effective, and inexpensive,
at the expense of durability.
        Medela recommends that the Pump in Style not be used by more than one
mother, because of potential, theoretical contamination concerns because
the kits are not closed systems, and there is no way to clean the
interior of the pump.  It is also not as durable as their hospital grade
machines, for the same reasons as above.
        Hope this answers your questions.

Elisheva,
        I do explain to mothers that the personal pumps are expected to last
about a year, not indefinately, to help them make their decision about
what pump is best for their situation.  I share the info from the
manufacturer if women are considering using one that was passed down to
them by a friend.
--
Catherine Watson Genna, IBCLC  New York City  mailto:[log in to unmask]

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