The two strategies "test then treat with amantadine" and "test then treat with rimantadine" were dominated, that is, they were both more costly and less effective than the other strategies.
The two strategies "treat with rimantadine" and "test then treat with oseltamivir or zanamivir" were dominated because they were less cost-effective than treatment with zanamivir.
Compared with "no testing or treatment", the incremental cost-effectiveness ratio (ICER) of amantadine therapy was $9.06 per day of illness avoided and $11.60 per quality-adjusted day gained.
Compared with amantadine treatment, the ICER of zanamivir therapy was $198 per day of illness avoided and $185 per quality-adjusted day gained.
If oseltamivir was substituted for zanamivir, the ICER was $252 per day of illness avoided and $235 per quality-adjusted day gained.
When the third-party perspective was taken, the ICERs were unchanged.
In elderly patients who required reduced dosage, rimantadine cost $128 per quality-adjusted day gained compared with amantadine.
In younger patients, amantadine was preferred if the likelihood of influenza A was greater than 67%, otherwise, neuraminidase inhibitors were preferred.
Testing strategies were more costly and less effective when the influenza probability was greater than 30%.
"No testing or treatment" was preferred if the influenza probability was less than 32% and the influenza utility was greater than 0.77.
In elderly patients, amantadine was favoured over rimantadine if the utility of medication side effects was greater than 0.94.
If society or third-party payers were willing to pay ($100 per quality-adjusted day gained, then amantadine or no treatment was preferred in all scenarios.
If the willingness-to-pay was $200 to $300, neuraminidase inhibitors were preferred in younger patients and rimantadine was preferred in elderly patients.
If the willingness-to-pay was $500 or more per quality-adjusted day gained, neuraminidase therapy was preferred.