539. Evolution of the 2009 Influenza A/H1N1 Virus Strains During Four Sequential Seasons After the Epidemic in Mexico: Implications on Disease Severity
Session: Poster Abstract Session: Respiratory Viruses
Thursday, October 8, 2015
Room: Poster Hall
Background: Mexico was the epicenter of the novel influenza A/H1N1 2009 pandemic. This study evaluates the evolution of influenza A/H1N1 pdm09 virus strains and the characteristics of associated-illness during sequential influenza seasons after the pandemic. 

Methods: From April 2010-April 2014, a cohort of 5662 children and adults who sought medical care for influenza-like illness (ILI) at six tertiary-care hospitals in Mexico, was prospectively followed over a period of 28 days to describe the clinical characteristics and outcomes of the disease.  Nasopharyngeal swabs were obtained at enrollment and tested by real-time reverse-transcription polymerase chain reaction (RT-qPCR) for influenza and a multiplex PCR for 19 respiratory pathogens.  

Results:

Of 5630 patients with ILI who underwent virological testing, influenza was confirmed in 919 (16%): 14% in children <18 years old and 17% in adults. Influenza A/H3N2 and A/H1N1pdm09 winter peaks alternated; influenza A/H1N1 pdm09 virus strains predominated during the 2011-2012 and the 2013-2014 seasons. The majority of influenza A/H1N1 pdm09 detections were in very young children (54%) and in young adults (46%). Conversely, detection of A/H3N2 was highest in the elderly (48%). Twenty of 28 (71%) influenza deaths were associated to A/H1N1 pdm09. Risk of influenza-associated hospitalization (OR 1.84; 95% CI 1.2, 2.7; p<0.001), intensive care admission (OR 2.95; 95% CI 1.2, 8.4; p=0.01) and death (OR 5.35; 95% CI 1.5, 28.6; p=0.003) increased during the 2013-2014 A/H1N1 pdm09 season as compared to the 2011-2012 season. Phylogenetic analyses showed that influenza A/H1N1 pdm09 virus strains responsible for the 2013-2014 winter peak diverged apart from those strains causing disease during the 2009 epidemic and from those included in the recommended vaccine. Several mutations of the hemagglutinin gene were detected, 3 located in the antigenic region (K166Q, S188T and S206T).

Conclusion: In Mexico, influenza A/H1N1 pdm09 circulates with seasonal A/H3N2 and B viruses during alternate winter seasons, increasing the risk of severe disease and mortality attributable to influenza.   Currently, influenza A/H1N1 pdm09 viruses do not match well with the 2015-2016 Northern Hemisphere recommended vaccine formulation.

M. Lourdes Guerrero Almeida, MD, MS, Infectious Diseases, Instituto Nacional de Ciencias Médicas y Nutrición, Salvador Zubirán, Mexico City, Mexico, Pilar Ramos-Cervantes, BS, Infectious Diseases, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Mexico City, Mexico, Arturo Galindo-Fraga, MD, MS, Hospital Epidemiology and Medical Care Quality Control, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Mexico City, Mexico, Daniel Noyola, MD, Facultad de Medicina, Universidad Autonoma de San Luis Potosi, San Luis Potosi, Mexico, Alejandra Ramirez-Venegas, MD, Pulmonologist, Instituto Nacional de Enfermedades Respiratorias, Mexico, Mexico, Rafael Valdez-Vazquez, MD, Infectious Diseases, Hospital General Dr. Manuel Gea Gonzalez, Mexico City, Mexico, Beatriz Llamosas-Gallardo, MD, Instituto Nacional de Pediatría, Mexico, Mexico, Ana Alejandra Ortiz-Hernández, MD, Instituto Nacional de Pediatría, Mexico City, Mexico, Sarbelio Moreno-Espinosa, MD, MS, Infectious Diseases, Hospital Infantil de México, Mexico City, Mexico, Ana Esthela Gamiño, MD, MS, Hospital Infantil de México, Mexico City, Mexico, Martin Magaña, MD, Hospital Central Dr. Ignacio Morones Prieto, San Luis Potosi, Mexico, Laura Freimanis, MD, PhD, Westat Inc., Rockville, MD, Hugo Arroyo-Figueroa, BS, NCC, Mexico Emerging Infectious Diseases Clinical Research Network, Mexico City, Mexico, Juan Francisco Galán-Herrera, MD, MS, Mexico Emerging Infectious Diseases Clinical Research Network, Mexico City, Mexico, Dean Follmann, PhD, National Institute of Allergy and Infectious Diseases, Bethesda, MD, John Beigel, MD, Leidos Biomedical Research, Inc. In support of clinical research section NIAD, National Institutes of Health, Bethesda, MD and Guillermo Ruiz-Palacios, MD, FIDSA, Comisión Coordinadora de Institutos Nacionales de Salud y Hospitales de Alta Especialidad, Mexico, Mexico

Disclosures:

M. L. Guerrero Almeida, None

P. Ramos-Cervantes, None

A. Galindo-Fraga, None

D. Noyola, None

A. Ramirez-Venegas, None

R. Valdez-Vazquez, None

B. Llamosas-Gallardo, None

A. A. Ortiz-Hernández, None

S. Moreno-Espinosa, None

A. E. Gamiño, None

M. Magaña, None

L. Freimanis, None

H. Arroyo-Figueroa, None

J. F. Galán-Herrera, None

D. Follmann, None

J. Beigel, None

G. Ruiz-Palacios, None

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