Changes in epidemiology, clinical features and severity of influenza A (H1N1) 2009 pneumonia in the first post-pandemic influenza season

Abstract

Although the influenza A (H1N1) 2009 virus is expected to circulate as a seasonal virus for some years after the pandemic period, its behaviour cannot be predicted. We analysed a prospective cohort study of hospitalized adults with influenza A (H1N1) 2009 pneumonia at 14 teaching hospitals in Spain to compare the epidemiology, clinical features and outcomes of influenza A (H1N1) 2009 pneumonia between the pandemic period and the first post-pandemic influenza season. A total of 348 patients were included: 234 during the pandemic period and 114 during the first post-pandemic influenza season. Patients during the post-pandemic period were older and more likely to have chronic obstructive pulmonary disease, chronic kidney disease and cancer than the others. Septic shock, altered mental status and respiratory failure on arrival at hospital were significantly more common during the post-pandemic period. Time from illness onset to receipt of antiviral therapy was also longer during this period. Early antiviral therapy was less frequently administered to patients during the post-pandemic period (22.9% versus 10.9%; p 0.009). In addition, length of stay was longer, and need for mechanical ventilation and intensive-care unit admission were significantly higher during the post-pandemic period. In-hospital mortality (5.1% versus 21.2%; p <0.001) was also greater during this period. In conclusion, significant epidemiological changes and an increased severity of influenza A (H1N1) 2009 pneumonia were found in the first post-pandemic influenza season. Physicians should consider influenza A (H1N1) 2009 when selecting microbiological testing and treatment in patients with pneumonia in the upcoming influenza season.

The first, second and third wave of pandemic influenza A (H1N1)pdm09 in North Denmark Region 2009–2011: a population‐based study of hospitalizations

“…A majority of hospitalized patients requiring therapy in ICUs were adults <65 years who on admission had respiratory failure due mainly to primary influenza pneumonia in agreement with other observations,8, 15, 21, 22, 23, 24 and in clear contrast to seasonal influenza. The number of patients that are admitted to an ICU may vary related to criteria used by the institution.…”

“…Experiences with the two other pandemics of the past century, 1957 and 1968, revealed patterns of varying severity,4 so it is of crucial importance to observe detailed patterns of hospitalization and mortality of any new pandemic strain. However, our results could be supported by recent studies from the US and Spain of a higher mortality of hospitalized H1N1pdm09 patients in the post‐pandemic season 7, 8. Nevertheless, in other countries with a very high mortality, the results may be different 9.…”

Morbilidad y mortalidad asociada a hospitalizaciones por influenza pandémica A (H1N1) 2009 en dos hospitales de la Región Metropolitana y evaluación de su impacto económico

“…Además, 16% de los pacientes presentó hipotensión arterial al ingreso, un elemento clínico no asignado históricamente a pacientes con infección pulmonar de origen viral, excepto en el caso de pacientes con infección por hantavirus 12 . El shock hemodinámico fue detectado en 3 de 99 pacientes (~3%) que ingresaron a una clínica privada de la RM el primer año de la pandemia 5 , en 20% de 20 hospitalizados en el sur de Chile y en grandes series de pacientes con influenza A (H1N1) 2009 se han reportado cifras de shock hemodinámico entre 1,7 y 8,8% de la población bajo estudio 2,13,14 . Ello genera imperfecciones del sistema de puntuación CURB-65 para reconocer casos graves por influenza.…”

“…Desde la perspectiva del laboratorio, la trombocitopenia y el aumento en los valores de LDH, presentes entre 20 y 24% de estos casos, también han sido descritos en otras series, incluso con frecuencias más elevadas (42% y valores promedio de 744-945 U/L, respectivamente) y asociados a mayor gravedad, extensión del compromiso pulmonar, riesgo de ingreso a UCI o muerte 11,13,16,17 . Estas alteraciones de laboratorio cuestionan la supuesta distinción entre infecciones virales y bacterianas 18 y están en línea con el hallazgo de leucocitosis, neutrofilia y valores elevados de PCR en estos pacientes, los que también han sido descritos en otras series de pacientes con influenza A (H1N1) 2009 14,17,19 .…”

“…La proporción de pacientes que ingresa a UCI ha sido variable en la literatura médica con rangos de 22,6 a 43% 14,17 y de 12,8 a 27,7% para conexión a VM 11,14 . No obstante esta dispersión, las tasas de letalidad hospitalaria observadas en este trabajo (16%) están en línea con lo reportado por otros autores (15 a 17%) 11,17 pero difieren con la ausencia de casos letales observados en dos clínicas privadas en la RM de Chile 4,5 , lo que en al menos un caso es explicado por el bajo perfil de co-morbilidad y gravedad incluido en la serie 5 .…”