Abstract
BackgroundIn 2009 a new influenza serotype (AH1N1) was identified in Mexico that spread rapidly generating worldwide alarm. San Luis Potosi (SLP) was the third state with more cases reported in that year. The clinical identification of this flu posed a challenge to medical staff. This study aimed at estimating the AH1N1 infection, hospitalization and mortality rates, and at identifying related clinical features in persons who received medical care during the influenza pandemic.MethodsRetrospective study with persons with flu-like illness who received public or private medical care in SLP from 15.03.09 to 30.10.09. Physicians purposely recorded many clinical variables. Samples from pharyngeal exudate or bronchoalveolar lavage were taken to diagnose AH1N1 using real-time PCR. Clinical predictors were identified using multivariate logistic regression with infection as a dependent variable. Odds ratios (OR) with 95% confidence intervals (CI) were computed. Analyses were stratified by age group based on the distribution of positive cases.ResultsFrom the 6922 persons with flu symptoms 6158 had available laboratory results from which 44.9% turned out to be positive for AH1N1. From those, 5.8% were hospitalized and 0.7% died. Most positive cases were aged 5–14 years and, in this subgroup, older age was positively associated with A H1N1 infection (95% CI 1.05-1.1); conversely, in patients aged 15 years or more, older age was negatively associated with the infection (95% CI 0.97-0.98). Fever was related in those aged 15 years or more (95% CI 1.4-3.5), and headache (95% CI 1.2-2.2) only in the 0–14 years group. Clear rhinorrhea and cough were positively related in both groups (p < 0.05). Arthralgia, dyspnea and vaccination history were related to lesser risk in persons aged 15 years or more, just as dyspnea, purulent rhinorrhea and leukocytosis were in the 0–14 years group.ConclusionThis study identified various signs and symptoms for the clinical diagnosis of AH1N1 influenza and revealed that some of them can be age-specific.
Highlights
In 2009 a new influenza serotype (AH1N1) was identified in Mexico that spread rapidly generating worldwide alarm
In the last century three pandemics reached the equivalent of Category 2 on the CDC pandemic severity index, and all were attributed to the subtype A [1]: The Spanish flu (AH1N1) from 1918–1920 disseminated in Europe and the US causing about 50 million deaths [3,5,6,8]; the Asian flu (AH2N2) from 1957–1958, responsible for 1–4 million deaths, was caused by a viral mutation that resulted in a combination of avian and human strains; and the Hong Kong flu (AH3N2) from 1968–1969 that resulted from an antigenic shift caused nearly 1 million deaths [5,8]
Study design This study retrospectively investigated data gathered on patients suspected to be infected by AH1N1 virus during the 2009 outbreak and for which a set of clinical data was systematically collected
Summary
In 2009 a new influenza serotype (AH1N1) was identified in Mexico that spread rapidly generating worldwide alarm. Influenza A virus is a main cause of winter epidemics that results in increments in respiratory morbidity. It constitutes a public health concern due to the burden that it represents for the health system and labor market, and for its potential to evolve into a pandemic [1,2,3]. In the last century three pandemics reached the equivalent of Category 2 on the CDC pandemic severity index (case-fatality ratio >0.1%), and all were attributed to the subtype A [1]: The Spanish flu (AH1N1) from 1918–1920 disseminated in Europe and the US causing about 50 million deaths [3,5,6,8]; the Asian flu (AH2N2) from 1957–1958, responsible for 1–4 million deaths, was caused by a viral mutation that resulted in a combination of avian and human strains; and the Hong Kong flu (AH3N2) from 1968–1969 that resulted from an antigenic shift caused nearly 1 million deaths [5,8]
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