Rodolfo Acuna-Soto

Mortality Patterns Associated with the 1918 Influenza Pandemic in Mexico: Evidence for a Spring Herald Wave and Lack of Preexisting Immunity in Older Populations

BACKGROUND Although the mortality burden of the devastating 1918 influenza pandemic has been carefully quantified in the United States, Japan, and European countries, little is known about the pandemic experience elsewhere. Here, we compiled extensive archival records to quantify the pandemic mortality patterns in 2 Mexican cities, Mexico City and Toluca. METHODS We applied seasonal excess mortality models to age-specific respiratory mortality rates for 1915-1920 and quantified the reproduction number from daily data. RESULTS We identified 3 pandemic waves in Mexico City in spring 1918, autumn 1918, and winter 1920, which were characterized by unusual excess mortality among people 25-44 years old. Toluca experienced 2-fold higher excess mortality rates than Mexico City but did not experience a substantial third wave. All age groups, including that of people 65 years old, experienced excess mortality during 1918-1920. Reproduction number estimates were <2.5, assuming a 3-d generation interval. CONCLUSION Mexico experienced a herald pandemic wave with elevated young adult mortality in spring 1918, similar to the United States and Europe. In contrast to the United States and Europe, there was no mortality sparing among Mexican seniors 65 years old, highlighting potential geographical differences in preexisting immunity to the 1918 virus. We discuss the relevance of our findings to the 2009 pandemic mortality patterns.

The 1918-19 Influenza Pandemic in Boyacá, Colombia

Timing of pandemic onset and prior immunity of populations varied by region.

Influenza and Pneumonia Mortality in 66 Large Cities in the United States in Years Surrounding the 1918 Pandemic

The 1918 influenza pandemic was a major epidemiological event of the twentieth century resulting in at least twenty million deaths worldwide; however, despite its historical, epidemiological, and biological relevance, it remains poorly understood. Here we examine the relationship between annual pneumonia and influenza death rates in the pre-pandemic (1910–17) and pandemic (1918–20) periods and the scaling of mortality with latitude, longitude and population size, using data from 66 large cities of the United States. The mean pre-pandemic pneumonia death rates were highly associated with pneumonia death rates during the pandemic period (Spearman ρ = 0.64–0.72; P<0.001). By contrast, there was a weak correlation between pre-pandemic and pandemic influenza mortality rates. Pneumonia mortality rates partially explained influenza mortality rates in 1918 (ρ = 0.34, P = 0.005) but not during any other year. Pneumonia death counts followed a linear relationship with population size in all study years, suggesting that pneumonia death rates were homogeneous across the range of population sizes studied. By contrast, influenza death counts followed a power law relationship with a scaling exponent of ∼0.81 (95%CI: 0.71, 0.91) in 1918, suggesting that smaller cities experienced worst outcomes during the pandemic. A linear relationship was observed for all other years. Our study suggests that mortality associated with the 1918–20 influenza pandemic was in part predetermined by pre-pandemic pneumonia death rates in 66 large US cities, perhaps through the impact of the physical and social structure of each city. Smaller cities suffered a disproportionately high per capita influenza mortality burden than larger ones in 1918, while city size did not affect pneumonia mortality rates in the pre-pandemic and pandemic periods.

The 1918 influenza pandemic in Florianopolis: A subtropical city in Brazil

Few studies have addressed the impact and dynamics of the 1918-1919 influenza pandemic in tropical and sub-tropical areas. To help cover this gap, we analyzed all death certificates issued from October 1913 to June 1921 in Florianopolis (Brazil), a subtropical state capital with a population of 41,298 inhabitants in 1920. In November and December 1918 (spring) there were a total of 70 and 14 deaths due to influenza and pneumonia, respectively, in contrast to a mean annual mortality attributed to these causes of 8.1 deaths, usually concentrated between January and August (summer to winter). We also determined the mortality burden due to the pandemic through the analysis of excess mortality during the pandemic period against the baseline mortality in the same months from other years. We obtained a total of 127 deaths (0.33% of the total population), nearly twice the number of deaths documented by death certificates from this period. No other influenza pandemic waves were detected in earlier or subsequent months. Our results confirm the observed patterns of age-shift in mortality in pandemic scenarios, with young adults as the most affected age-group. The pandemic in Florianopolis was further characterized by some specific outcomes: (1) there was a discrete peak in mortality due to renal causes in the initial phase of the pandemic; (2) pandemic influenza did not affect the number of reported bronchitis and bronchiolitis deaths (unusually high in the year preceding the pandemic); and (3) the mortality burden was proportionally lower in Florianopolis than in large urban centers such as São Paulo and Rio de Janeiro. We suggest that this latter outcome was the result of an effective and prompt network of voluntary solidarity assistance (as endorsed by contemporaneous documents), which was probably more difficult to implement in larger metropolis.

Drought and Epidemic Typhus, Central Mexico, 1655-1918

Epidemic typhus is an infectious disease caused by the bacterium Rickettsia prowazekii and transmitted by body lice (Pediculus humanus corporis). This disease occurs where conditions are crowded and unsanitary. This disease accompanied war, famine, and poverty for centuries. Historical and proxy climate data indicate that drought was a major factor in the development of typhus epidemics in Mexico during 1655–1918. Evidence was found for 22 large typhus epidemics in central Mexico, and tree-ring chronologies were used to reconstruct moisture levels over central Mexico for the past 500 years. Below-average tree growth, reconstructed drought, and low crop yields occurred during 19 of these 22 typhus epidemics. Historical documents describe how drought created large numbers of environmental refugees that fled the famine-stricken countryside for food relief in towns. These refugees often ended up in improvised shelters in which crowding encouraged conditions necessary for spread of typhus.

Death Records from Historical Archives: A Valuable Source of Epidemiological Information

In almost every geographic location around the world, historic archives store a wealth of valuable epidemiological information. Mostly scrutinized by social scientists, historic information has an enormous potential for epidemiologic research, yet this information remains largely forgotten. This situation is starting to change. A renewed interest in historic data has flourished as recent reports, based on the information retrieved from historic records, have demonstrated that the information stored in historic archives is of an exceptional quality. Initially studied by a few intrepid epidemiologists, the field is growing vigorously. The application of quantitative methods and geographic information systems to historical data is producing a more detailed picture of the dynamics of human disease in space and time.

The Fate of Historical Death Certificates: The Silent Burning of Another Library of Alexandria

Ever since societies created registration systems of their citizens, they also provided something literally transcendental to each individual—a lasting record of their existence. Today these documents are not only a testimony of a person’s life but also precious sources of knowledge to understand the workings of diseases that still haunt us. For instance, the understanding of secular trends in maternal mortality,1 and the identification of early warnings of influenza pandemics2 were only possible thanks to the information on historical death certificates kept in archives, cemeteries, and churches.3 The recent study by Brosco4 on the history of medical care for children in the United States also illustrates nicely the importance of vital statistics preservation and how this information contributed to improving pediatric health policies in this country. Unfortunately, the uniqueness and fragility of (mostly) paper collections, often kept in less than ideal conditions (Figure 1), make them a silently vanishing treasure. Although well preserved in some countries,3 we witnessed the advanced stages of deterioration or disposal of entire vital statistics collections in several regions of the world because of improper storage, mishandling, natural disasters, or active disposal. The permanent loss of these documents is a silent yet ongoing process3 that persists with little awareness of public authorities and, more critically, from those sectors of the scientific community that will otherwise miss the opportunity to develop retrospective studies in geographically diverse contexts. FIGURE 1— Historical death certificates kept in a cemetery—a fragile treasure. Still, the increasing availability of affordable technologies for collecting and curating data in a long-lasting format now makes it possible to address the preservation of this global heritage. Printed material can now be easily digitized even in remote settings and preserved in virtual libraries. For example, as part of our studies on past pandemics,5 a student digitized 10 years of death certificates from a Brazilian city, revealing novel aspects of the 1918 influenza pandemic. Additionally, the density of information showed that smallpox mortality had been largely underestimated in the 1920s. More important, this digital material is now preserved in the local public archive. Similarly precious data could be stored on digital repositories to facilitate long-term access. Whereas the challenges of maintaining digital information can be addressed with technical solutions, nothing can be done when a unique source of knowledge is irreversibly lost. This is as true for the scrolls lost in the fire that destroyed the Library of Alexandria as it is for the vanishing volumes of certificates around the world today.

Influenza seasonality goes south in the Yucatan Peninsula: The case for a different influenza vaccine calendar in this Mexican region

INTRODUCTION While vaccination may be relatively straightforward for regions with a well-defined winter season, the situation is quite different for tropical regions. Influenza activity in tropical regions might be out of phase with the dynamics predicted for their hemispheric group thereby impacting the effectiveness of the immunization campaign. OBJECTIVE To investigate how the climatic diversity of Mexico hinders its existing influenza immunization strategy and to suggest that the hemispheric vaccine recommendations be tailored to the regional level in order to optimize vaccine effectiveness. METHODS We studied the seasonality of influenza throughoutMexico by modeling virological and mortality data.De-trended time series of each Mexican state were analyzed by Fourier decomposition to describe the amplitude and timing of annual influenza epidemic cycles and to compare with each the timing of the WHOs Northern and Southern Hemispheric vaccination schedule. FINDINGS The timings of the primary (major) peaks of both virological and mortality data for most Mexican states are well aligned with the Northern Hemisphere winter (December-February) and vaccine schedule. However, influenza peaks in September in the three states of the Yucatan Peninsula. Influenza-related mortality also peaks in September in Quintana Roo and Yucatan whereas it peaks in May in Campeche. As the current timing of vaccination in Mexico is between October and November, more than half of the annual influenza cases have already occurred in the Yucatan Peninsula states by the time the Northern Hemispheric vaccine is delivered and administered. CONCLUSION The current Northern Hemispheric influenza calendar adopted for Mexico is not optimal for the Yucatan Peninsula states thereby likely reducing the effectiveness of the immunization of the population. We recommend that Mexico tailor its immunization strategy to better reflect its climatologic and epidemiological diversity and adopt the WHO Southern Hemisphere influenza vaccine and schedule for the Yucatan Peninsula.

A perspective on the 2009 A/H1N1 influenza pandemic in Mexico.

In this article, we provide a chronological description of the 2009 H1N1 influenza pandemic in Mexico from the detection of severe respiratory disease among young adults in central Mexico and the identification of the novel swine-origin influenza virus to the response of Mexican public health authorities with the swift implementation of the National Preparedness and Response Plan for Pandemic Influenza. Furthermore, we review some features of the 2009 H1N1 influenza pandemic in Mexico in relation to the devastating 1918-1920 influenza pandemic and discuss opportunities for the application of mathematical modeling in the transmission dynamics of pandemic influenza. The value of historical data in increasing our understanding of past pandemic events is highlighted.

A Critical Assessment of Officially Reported Chagas Disease Surveillance Data in Mexico.

Objective. Chagas disease, a disease caused by Trypanosoma cruzi, disproportionately affects poor people throughout Latin America. In Mexico, assessments of officially reported burden have not been previously reported. To evaluate discontinuity between surveillance data and data from other sources, we used data from the Mexican Ministry of Health to describe the distribution of reported Chagas disease over time in Mexico and compare it with estimates from the literature. Methods. We summarized age and sex differences for Chagas cases and mortality for 1995–2013 and 1982–2010, respectively. We examined the spatial distribution of Chagas disease over time with respect to disease burden. We further compared officially reported figures with estimates from the literature. Results. Among 6,494 officially reported cases, rates of Chagas disease were highest in adults aged 25–44 years (47.3%). Mortality was highest in adults aged ≥45 years (423/495, 85.5%). The data indicated increasing temporal trends for incidence and mortality. The greatest burden occurred in southern states, with increasing spatial distribution over time. Fewer than 900 cases and 40 deaths were officially reported annually, in contrast to estimates from the literature of approximately 69,000 new cases and 25,000 deaths annually. Conclusion. While increasing trends in officially reported data have been observed, large discrepancies in case estimates compromise our understanding of Chagas disease epidemiology. Reported cases based on current practices are not enough to correctly assess the Chagas disease burden and spatial distribution in Mexico. Understanding the true epidemiology of this disease will lead to more focused and successful control and prevention strategies to decrease disease burden.