50% of cases in the 1918 Pandemic Flu had co-morbidity (both influenza and bacterial infections) in the 2009 Pandemic Flu (H1N1) 33% had co-morbidity with bacterial infections.
[link to jama.jamanetwork.com]

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ABSTRACT

Bacterial coinfection complicated nearly all influenza deaths in the 1918 influenza pandemic and up to 34% of 2009 pandemic influenza A(H1N1) infections managed in intensive care units worldwide. More than 65 000 deaths attributable to influenza and pneumonia occur annually in the United States. Data from 683 critically ill patients with 2009 pandemic influenza A(H1N1) infection admitted to 35 intensive care units in the United States reveal that bacterial coinfection commonly occurs within the first 6 days of influenza infection, presents similarly to influenza infection occurring alone, and is associated with an increased risk of death. Pathogens that colonize the nasopharynx, including Staphylococcus aureus, Streptococcus pneumoniae, and Streptococcus pyogenes, are most commonly isolated. Complex viral, bacterial, and host factors contribute to the pathogenesis of coinfection. Reductions in morbidity and mortality are dependent on prevention with available vaccines as well as early diagnosis and treatment."

In many of those cases, since the bacteria can't be cultured in time, unless the patient exibits symptoms of a bacterial infection, and many won't for awhile, then by the time the physician detects the bacteria, the patient can die with serious influenza plus bacterial infections like those above in bold.

In the 1918 Pandemic Flu, often in 24 hours, the patient might die.