Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Kongkam et al. 2009 (40) Case series report Morphine or other opioid and
nonopioid drugs Meningitis in 2 of 13 patients (15.4%); paraspinous abscess with
bacterial meningitis during IT pump use in one patient required pump removal; subclavian venous catheter sepsis and intracardiac fungal ball…
Category: