Pandemic influenza A (H1N1) in the North of Portugal: how did the autumn-winter wave behave?
BACKGROUND
In April 2009 the Centers for Disease Control and Prevention announced the identification of a novel influenza virus in two patients in California, called influenza A (H1N1) 2009. On 11 June 2009 the Director-General of the World Health Organization declared a pandemic of influenza A (H1N1). In Portugal the first case of pandemic influenza A (H1N1) was reported on 29th April and the Northern Region of the country registered the first cases soon after that.


OBJECTIVE
This report pretends to give an overview of the characteristics of Autumn/Winter pandemic wave in the North of Portugal.


RESULTS
A total of 64 195 cases of influenza-like illness were registered in public health services in the region between week 40, 2009 and week 4, 2010. The cumulative attack rate of those cases was 17.1/1 000 inhabitants. Most of the cases occurred in females and in the under 20 years. The peak of the Autumn/Winter wave was attained in week 48, but geographic and time distribution of the pandemic was heterogeneous in the region. Hospitalization rate for influenza-like illness cases in the population was higher for the under 10 years and decreased with age. Forty four deaths in pandemic influenza A (H1N1) laboratory-confirmed cases occurred in the region (mortality rate - 1.2/100 000) and the risk of death was lower in younger age groups. The peak of deaths occurred two weeks later than the peak of cases.


CONCLUSIONS
We can assume that the Autumn/Winter pandemic wave impact was mild in the Northern Region of Portugal. We consider the importance of pursuing and reinforcing influenza surveillance in the region.
Epidemiological Surveillance Unit, Department of Public Health, Northern Regional Health Administration, Ministry of Health, Porto, Portugal. acorreia@arsnorte.min-saude.pt
A M
AM
Correia
L
L
Queirós
J
J
Dias
D000293:Adolescent; D000328:Adult; D002648:Child; D005260:Female; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype; D007251:Influenza, Human / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D058873:Pandemics; D011174:Portugal / Q000453:epidemiology; D012621:Seasons; D055815:Young Adult