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Influenza, combined with bacterial pneumonia increases the risk of death more than threefold

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Influenza, together with bacterial pneumonia, could increase the risk of death by more than three times. Therefore, preventing bacterial pneumonia is especially important when an infection with the influenza virus occurs. These are the findings of a study published in the International Journal of Infectious Diseases, coordinated by the Virology and Innate Immunity Research Group at CEU San Pablo University (CEU USP), led by Dr. Estanislao Nistal Villán, in collaboration with the Immunology and Transplants Unit of the National Centre for Microbiology at the Carlos III Institute of Health (ISCIII), led by Dr. Jordi Ochando.

The lead authors are Javier Arranz-Herrero from the Immunology and Transplants Unit at CNM-ISCIII and CEU San Pablo University and Jesús Presa, also at the CEU San Pablo University School of Medicine. The study also involved collaboration from Dr. Jose Ángel Arranz from Gregorio Marañón Hospital, Dr. Antonio Lalueza from 12 de Octubre Hospital, Dr. María Escribese from CEU San Pablo University, and Dr. Vicente Soriano from the School of Health Sciences at the International University of La Rioja (UNIR).

Data of over 48.000 patients, published between 2010 and 2020, was analysed from 135 studies conducted in 28 countries in order to identify the main factors that increase the severity of influenza. The results were independently validated using the TrinetX platform with data from nearly four million patients and the findings show bacterial lung infections to be one of the most relevant risk factors in influenza infections.

"Some of the bacteria that cause these secondary pneumonias can live in our bodies and colonise our upper respiratory tract or infect us from the outside. The most common ones, such as Streptococcus pneumoniae and Staphylococcus aureus, are responsible for over 60% of bacterial pneumonias associated with influenza," explain Javier Arranz-Herrero and Jesús Presa.

Dr. Estanislao Nistal Villán points out that the analysis provides particularly interesting data, such as the fact that influenza, combined with bacterial lung infection, increases the risk of death by over three times. The researchers also found that some chronic hematologic diseases pose a similar risk, followed by the risk associated with neurological disorders, renal failure, immunosuppression, chronic liver or cardiovascular diseases, as well as other conditions.


One of the key factors to prevent bacterial pneumonia

The study also suggests that bacterial complications in cases of influenza may be underdiagnosed, highlighting the need to implement strategies for prevention, diagnosis, and antibiotic treatment in cases where there is a high risk of complications associated with influenza infections.

Influenza is a disease caused by different Influenza viruses: "Despite how accustomed we are to the word 'flu,' this disease is associated with more deaths in Spain than those caused by traffic accidents. There are various physical conditions, age factors, or diseases that increase the risk of complications and death in patients who develop influenza," adds Nistal Villán.

The impact of bacterial infections associated with influenza cases may be behind the high fatality rate of the 1918 pandemic: "More than 90% of lung autopsies analysed from influenza-related deaths during the 1918 pandemic showed a high presence of bacteria, something that could be associated with a higher mortality rate than that caused solely by viral infection," the authors point out. In this regard, the results suggest that prevention through vaccination, along with public health containment measures, early diagnosis and proper treatment of bacterial infections to prevent the possible emergence of other bacteria that are increasingly resistant to antibiotics, are all key factors in improving the prognosis of patients with influenza infections.

The current COVID-19 crisis has highlighted the urgent need to develop new strategies that improve our healthcare system to identify and reduce specific risks, the researchers also note. Children and the elderly are the groups most at risk of suffering complications from influenza: " This study aims to highlight with specific values the weaknesses that must be taken into account to provide better care against the flu," conclude the authors of the study.

Article reference: Javier Arranz-Herrero, Jesús Presa, Sergio Rius-Rocabert, Alberto Utrero-Rico, José Ángel Arranz-Arija, Antonio Lalueza, María Marta Escribese, Jordi Ochando, Vicente Soriano, Estanislao Nistal-Villan, "Determinants of poor clinical outcome in patients with influenza pneumonia: a systematic review and meta-analysis," International Journal of Infectious Diseases (2023), doi:

Palabras clave Influenza Bacterial Pneumonia Research Virology Immunity