Yes, it is VERY possible that HCQ was given only to the sicker patients. When a study says “retrospective” (which it does) that means the above is possible.
You can only have confidence in randomized double-blind studies, and this one doesn’t qualify.
A couple of weeks ago I saw an article saying that - for unspecified reasons - American doctors were not prescribing the HCQ cocktail as early as doctors in other countries. If the doctors in this study held off using HCQ until everything else failed, that might explain the poor results.
It is not just very possible, the authors state it clearly:
However, hydroxychloroquine, with or without azithromycin, was more likely to be prescribed to patients with more severe disease, as assessed by baseline ventilatory status and metabolic and hematologic parameters. Thus, as expected, increased mortality was observed in patients treated with hydroxychloroquine, both with and without azithromycin.
I suppose studies like this do have a value. They teach us how to get bad results from HCQ+AZ: wait as long as possible before starting the drug combo.
Meanwhile, back in France, Dr. Didier Raoult has continued to treat COVID-19 patients with HCQ+AZ. As of today, 2,999 COVID-19 patients have been treated with the drug combo. Among patients who received the drugs for more than three days, there have been 12 deaths.