A search of Joanna Briggs for the term piggyback identified several evidence summaries and recommendations.  Each of them cited the 2002 CDC guidelines as evidence in discussing piggyback systems.

MMWR Recomm Rep. 2002 Aug 9;51(RR-10):1-29.
O’Grady NP, et al.  Guidelines for the prevention of intravascular catheter-related infections. Centers for Disease Control and Prevention.

On p. 11, the guidelines state that “modified piggyback systems have the potential to prevent contamination…” and cite this single study:

JPEN J Parenter Enteral Nutr. 1992 Nov-Dec;16(6):581-5.
Inoue Y, et al.  Prevention of catheter-related sepsis during parenteral nutrition: effect of a new connection device.

A search of PubMed was conducted using the following terms:
(piggyback OR secondary iv OR (secondary AND infusion)) AND infections AND prevention AND central venous catheters

The results include the Inoue study.  No other studies focus on prevention of catheter-associated bloodstream infections, but may report data on infection rates, which may also be useful.  However, the populations for most of the other studies were neonates.

jkn 3/14