Quantifying the mortality caused by the H1N1 influenza virus during the 2009 pandemic in Mexico

Abstract

Introduction: The frequency and mortality of the pandemic caused by influenza A(H1N1)pdm09 might have been underestimated, especially in developing countries. This study was designed to quantify the possible underestimation of pandemic influenza mortality and evaluate the concordance between the data reported for A(H1N1)pdm09 mortality and the causes of death reported during the pandemic period of April 2009 to February 2010. Methodology: The death certificates of 754 confirmed cases of A(H1N1)pdm09 infection were included in the study. Data was analyzed using the United States Centers for Disease Control and Prevention's statistical model accounts for the variability in the proportion at each step using the Monte Carlo probabilistic model sampled from a uniform probability distribution. Results: A total of 1,969 deaths were estimated, with an estimated lethality of 5.53 per 100,000 (range, 3.5-8.76 per 100,000) in contrast with the 754 deaths and a lethality of 1.98 per 100,000 infected patients officially reported. In 631 of 754 (83.7%) death certificates from A(H1N1)pdm09 influenza-positive patients, influenza was not mentioned as a cause of death. Conclusions: It is possible that the mortality of the pandemic was three times higher than officially reported in Mexico. One source of error that could explain this underestimation is in the completion of death certificates, because in > 80% of confirmed cases of infection with influenza virus, it was not reported as the cause of death.

Comparative epidemiology between the 2009 H1N1 influenza and COVID-19 pandemics

“…Although some studies only show that about half of deaths from the disease have other cofactors, it is important to note that the incidence of comorbidity increases with age, but the incidence of influenza tended to be higher in young groups. The most common comorbidities identified in patients who died of A H1N1 influenza were hypertension (23%), diabetes (5.7%), obesity (4.2%), neurological diseases (4%), renal failure (3.8%), and pneumopathy (3.7%) [ 35 , 36 ].…”

Influenza Burden and Transmission in the Tropics

“…The asterisk indicates a study period that did not cover an entire season or year. IHD refers to ischemic heart disease (Wu et al [ 35 ], Freitas et al [ 25 ], Echevarria-Zuno et al [ 20 ], Charu et al [ 26 ], Homaria et al [ 36 ], Cerbino Neto et al [ 37 ], Fowlkes et al [ 38 ], Wu et al [ 27 ], Perez-Flores et al [ 39 ], Comas-Garcia et al [ 24 ], Fajardo-Dolci et al [ 40 ], Saborio et al [ 19 ], Yang et al [ 33 ], Bunthi et al [ 41 ]) …”

Cause of death in hospitalized patients with laboratory-confirmed influenza

“…As observed in previous studies, a virological diagnosis of influenza does not necessarily mean that influenza is recorded as the underlying cause of death, thus underestimating influenza burden in the Statistics of Causes of Death 8,10,11 . Influenza can trigger secondary bacterial infections or exacerbate existing chronic conditions, and these comorbidities usually prevail as the underlying cause of death.…”

“…According to our results, 37% of the mortality in patients with laboratory-confirmed influenza would remain uncounted, and would only be identified by including all other causes of death in the analysis. Our study adds to others that support the need to consider all-cause mortality to estimate the total burden of influenza mortality 6,[11][12][13] . These results also suggest the importance of considering allcause deaths to quantify the total effect of the influenza vaccine on mortality.…”