Two thirds of these occur in low and middle income countries, the figures suggest.
The authors base their findings on 4000 articles written in English and published from 1976 onwards, which looked at substandard medical care given to hospital patients around the globe.
The researchers focused on seven key markers for substandard care: harm from prescribed medications; urinary tract infections associated with catheters; bloodstream infections associated with catheters; pneumonia acquired in hospital; blood clots (VTEs);falls; and bed sores.
They used an approach similar to the Global Burden of Disease (GBD) deployed by the World Health Organisation, to calculate the amount of suffering caused by individual diseases - to estimate the impact of unsafe care on subsequent years of life lost to death/disability (DALYs).
The most common type of substandard care involved medicines in high income countries, which occur in 5% of all hospital stays, while blood clots feature most often in low and middle income countries, occurring in 3%.
Based on the incidence of all seven aspects of unsafe care, the authors worked out that for every 100 hospital admissions, there were around 14.2 such cases in high income countries and 12.7 in low and middle income countries.
And they calculated that these caused 16.8 million instances of harm in high income countries and 25.9 million in low and middle income countries, resulting in close to 43 million adverse events as a result of unsafe care every year.
Furthermore, the authors calculated that there were some 22.6 million years of life lost to death or disability (DALYs) as a result.
But low and middle income countries bore the brunt, with twice as many (15.5 million) DALYs lost as in high income countries (7.2 million). Blood clots alone accounted for 5.4 million DALYs lost in low and middle income countries compared with 3.9 million in high income countries.
Premature death accounted for the largest proportion of DALYs lost to all seven aspects of unsafe care around the world - more than 78% in high income countries and more than 80% in low and middle income countries.
The authors note that lack of access to healthcare facilities presents its own dangers; nevertheless, all patients should be able to rely on safe and high quality care once admitted to hospital, they say.
"When patients are sick, they should not be further harmed by unsafe care," write the authors, adding: "This should be a major policy emphasis for all nations."
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