In 2009, we witnessed a pandemic of the previously unknown subtype influenza A (H1N1) virus (10
). The first confirmed cases in our hospital were in the 22nd
epidemiological week, and the majority of the admissions and confirmed cases occurred during the 30th
epidemiological week. In Brazil, the peak confirmation rate of cases was seen in the 31st
epidemiological week (7
During the pandemic, changes were made to the reporting and selection criteria for laboratorial diagnosis. In the 28th
epidemiological week, reporting was required only for the cases with severe acute respiratory distress syndrome or those with risk factors for worse outcomes (4
). At our hospital, the majority of hospitalizations occurred after this date.
In our study, the admitted children were younger than the non-admitted children. In Brazil, the age groups that had more frequent acute respiratory distress syndrome were children under age 2 and adults between the ages of 20 and 29 years (7
In concordance with other studies, the children who were admitted to our hospital with influenza A (H1N1) infection had a high prevalence of chronic disease, with a predominance of pneumopathy (5
),. However, we must consider that the high percentage found here might represent a bias because São Paulo Hospital is a tertiary hospital.
In this study, there were two deaths, two reversed cardiopulmonary arrests, one rejection of a transplanted kidney and an acute metabolic acidosis at the onset of diabetes mellitus type 1, all of which were critical cases. A recent Brazilian study demonstrated a more severe course of the disease in children infected with the H1N1 virus than in children with flu-like symptoms who received negative rapid tests for H1N1 (18
As observed in the United States (12
), Argentina (15
), Canada (17
), and in another Brazilian study (18
), most patients who were hospitalized with influenza A (H1N1) had complications, and many needed intensive care, despite immediate hospitalization from the emergency room and prompt oseltamivir initiation. Seventy-one percent of the hospitalized patients in our study started this medication more than 48 hours after the symptoms began. This delay could have contributed to a worsening of their clinical condition.
In this study, 27% of the 37 children who were hospitalized were admitted to the ICU, and 78% had some underlying disease. Likewise, among the first 272 patients hospitalized with influenza A (H1N1) reported in the United States, 25% were admitted to an ICU, and 73% had at least one underlying medical condition (12
During annual outbreaks of seasonal influenza, most patients who require hospitalization are at the extremes of age distribution. There are also a greater number of hospitalizations in patients with chronic diseases, such as diabetes, cardiovascular disease, neurological disease, and pulmonary disease (including asthma) (12
). A significant number of hospitalizations are caused by influenza every year (19
Despite a stable total number of hospital admissions in all pediatric units at our hospital in 2009 and 2010, there was a reduction in the hospital admissions of confirmed pediatric influenza A (H1N1) patients after the vaccination campaign in 2010. This result is in accordance with other data from our country (22
The total number of influenza A (H1N1) vaccine doses administered in Brazil was 89,580,203. The vaccination coverage for children under age 2 was 100% (5,580,671 vaccine doses) and 60% for the 2 to 4 year-old age group, with 5,202,438 vaccine doses given (23
Here, we have described influenza A (H1N1) pediatric cases admitted to a tertiary hospital in São Paulo, Brazil over two consecutive years. The striking decrease in the number of cases from 2009 to 2010 is likely an effect of the massive influenza A (H1N1) vaccination campaign in Brazil in 2010, along with the immunity acquired by the population because of the intense viral circulation.