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Background. The 1918‐1919 A/H1N1 influenza pandemic killed 50 million people worldwide. Historical records suggest that an early pandemic wave struck Europe during the summer of 1918. Methods. We obtained surveillance data that were compiled weekly, during 1910‐1919, in Copenhagen, Denmark; the records included medically treated influenza-like illnesses (ILIs), hospitalizations, and deaths by age. We used a Serfling seasonal regression model to quantify excess morbidity and mortality, and we estimated the reproductive number (R) for the summer, fall, and winter pandemic waves. Results. AlargeepidemicoccurredinCopenhagenduringthesummerof1918;theagedistributionofdeathswas characteristic of the 1918‐1919 A/H1N1 pandemic overall. That summer wave accounted for 29%‐34% of all excess ILIs and hospitalizations during 1918, whereas the case-fatality rate (0.3%) was many-fold lower than that of the fall wave (2.3%). Similar patterns were observed in 3 other Scandinavian cities. R was substantially higher in summer (2.0‐5.4) than in fall (1.2‐1.6) in all cities. Conclusions. TheCopenhagensummerwavemayhavebeencausedbyaprecursorA/H1N1pandemicvirusthat transmitted efficiently but lacked extreme virulence. The R measured in the summer wave is likely a better approximation of transmissibility in a fully susceptible population and is substantially higher than that found in previous US studies. The summer wave may have provided partial protection against the lethal fall wave. Recent studies of the 1918 “Spanish” influenza pan

Pregnancy has been identified as a risk factor for severe illness and death during all the influenza pandemics of the 20th century and in the 2009–2010 influenza A(H1N1) pandemic. In the 1957 influenza pandemic, ∼50% of the deaths in women of childbearing age occurred in pregnant women and resulted from primary viral pneumonia following influenza infection [1–3]. Similarly, although pregnant women comprise ∼1% of the US population today, they accounted for 5% of influenza-related deaths during the 2009 pandemic; furthermore, pregnant women were at elevated risk for admission to intensive care units and preterm delivery [4–6]. In contrast to the risk of maternal illness during pregnancy, the impact of influenza on the fetus and likelihood of miscarriage has been less studied [7]. Although studies have shown that maternal influenza vaccination improves fetal and infant outcomes [8, 9], little is known about whether maternal influenza infection has the potential to terminate pregnancies, and comprehensive data are lacking on the association between influenza and birth outcomes. This issue could have important implications for public health strategies and clinical care for pandemics as well as seasonal epidemics. Investigating the impact of influenza on pregnancy is a challenge, because miscarriages may not be directly linked to influenza when patients are referred to clinics, especially if miscarriage occurs several weeks after primary viral infection. In addition, early pregnancy loss may occur unbeknownst to women who have not yet discovered that they are pregnant. Clinical reports from the 1918 pandemic period support a link between influenza and elevated maternal morbidity, mortality, pregnancy loss, and preterm labor [10–12]. In a 1919 report of 1350 pregnant women with influenza, 26% of case subjects miscarried (the largest proportion in the first trimester), whereas 52% of pneumonia-complicated case subjects miscarried [13]. This phenomenon associated with the 1918 pandemic appears to have been geographically widespread; a preponderance of miscarriages following pandemic peak activity was described in the Philippines [14], and an increase in miscarriages in women 5–9 months pregnant followed by a baby boom was reported in Norway [15]. In more recent literature, a possible association was noted between seasonal influenza A(H3N2) and a cluster of miscarriages [16]. Small observational studies of pregnant women infected with the 2009 pandemic influenza A(H1N1) virus reported preterm deliveries and fetal deaths [17, 18]. Despite these geographically limited reports and case series, the association between maternal influenza and pregnancy loss has not been quantified. In this study, we utilized historical epidemiological records from the 1918 influenza pandemic in 3 Scandinavian countries and the United States to examine the relationship between influenza and pregnancy outcomes at the population level. We hypothesized that if influenza infection in pregnant women can cause miscarriages on a large scale, then a decline in births would occur within 9 months of the peak pandemic activity. Data from contemporaneous national surveillance systems were acquired from library archives to elucidate the potential temporal associations between influenza activity and birth patterns, and to quantify the risk of miscarriage associated with influenza infection.

We investigate cholera transmission using data from historical cholera epidemics. The results suggest short-cycle (household/institution level) transmission was important in early secondary transmission. This study of historical outbreaks can inform investigations in current cholera epidemic settings., Background Although cholera is considered the quintessential long-cycle waterborne disease, studies have emphasized the existence of short-cycle (food, household) transmission. We investigated singular Danish cholera epidemics (in 1853) to elucidate epidemiological parameters and modes of spread. Methods Using time series data from cities with different water systems, we estimated the intrinsic transmissibility (R0). Accessing cause-specific mortality data, we studied clinical severity and age-specific impact. From physicians’ narratives we established transmission chains and estimated serial intervals. Results Epidemics were seeded by travelers from cholera-affected cities; initial transmission chains involving household members and caretakers ensued. Cholera killed 3.4%–8.9% of the populations, with highest mortality among seniors (16%) and lowest in children (2.7%). Transmissibility (R0) was 1.7–2.6 and the serial interval was estimated at 3.7 days (95% confidence interval, 2.9–4.7 days). The case fatality ratio (CFR) was high (54%–68%); using R0 we computed an adjusted CFR of 4%–5%. Conclusions Short-cycle transmission was likely critical to early secondary transmission in historic Danish towns. The outbreaks resembled the contemporary Haiti outbreak with respect to transmissibility, age patterns, and CFR, suggesting a role for broader hygiene/sanitation interventions to control contemporary outbreaks.