gms | German Medical Science

18th Symposium on Infections in the Immunocompromised Host

International Immunocompromised Host Society

15. to 17.06.2014, Berlin

Influenza A H1N1: Five Years of Diagnostics in Brazil

Meeting Abstract

  • C.S. Lázari - Brazil
  • D.S. Pereira - Brazil
  • E.R.M. Silva - Brazil
  • J. de Sá - Brazil
  • J.L.M. Sampaio - Brazil
  • C.F.H. Granato - Brazil

18th Symposium on Infections in the Immunocompromised Host. Berlin, 15.-17.06.2014. Düsseldorf: German Medical Science GMS Publishing House; 2014. Doc14ichs19

doi: 10.3205/14ichs19, urn:nbn:de:0183-14ichs195

Veröffentlicht: 3. Juni 2014

© 2014 Lázari et al.
Dieser Artikel ist ein Open Access-Artikel und steht unter den Creative Commons Lizenzbedingungen (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.de). Er darf vervielfältigt, verbreitet und öffentlich zugänglich gemacht werden, vorausgesetzt dass Autor und Quelle genannt werden.


Gliederung

Text

Since 2009, when the novel H1N1 Influenza A was first detected, it has become the predominant influenza subtype in many countries. Data from the Global Influenza Surveillance and Response System (WHO) show that more than a half of the specimens positive for influenza in the Southern Hemisphere during 2013 corresponded to the A (H1N1)pdm09 subtype. In Brazil, the same trend has been confirmed last year: according to the Ministry of Health, during 2013, 21.4% of more than 16,500 respiratory specimens collected for surveillance purposes were positive for viruses. In the first 3 months of the year, a predominance of respiratory syncytial virus (RSV) has been verified, while influenza virus circulation increased from April up to the end of the winter. During this period, influenza A (H1N1)pdm09 was the commonest subtype. In the same year, 16.5% of notified cases of severe acute respiratory syndrome

were due to influenza virus; subtype A (H1N1)pdm09 was detected in 62.9% of them, and caused 80.3% of deaths attributed to influenza infection.

In order to provide additional epidemiologic data about influenza A (H1N1) pdm09 circulation in Brazil, we studied all results of detection of influenza A (H1N1)pdm09 by polymerase chain reaction (PCR) performed in a private laboratory since 2009.

Material and Methods: We retrospectively analyzed the results data bank of a Brazilian private laboratory located in the Southeastern city of São Paulo, the largest and most populated of Latin America. This lab analyzes samples from outpatients attendance and more than 10 hospitals in the main capitals of Brazil: São Paulo, Rio de Janeiro, Porto Alegre, Curitiba, Salvador and Recife. In addition, it is a reference for smaller laboratories, which implies in receiving samples from virtually all regions of the country. This laboratory is certified by the College of American Pathologists.

All clinical specimens collected from respiratory tract were included: swab, aspirate or lavage from nasopharynx, oropharynx or trachea; bronchial or bronchoalveolar lavage; and a small number of lung tissue fragments.

An RT-PCR has been performed according to the CDC protocol in all samples; they were considered positive for influenza A (H1N1) pdm09 virus if both the influenza A virus (InfA) primers that target the matrix gene and the respective subtype-specific primers recognizing either the swine influenza A virus nucleocapsid gene (swInfA) or the H1N1 swine influenza A virus hemagglutinin gene (swH1) had amplification curves which crossed the threshold (CT values) within 40 cycles. All runs included notemplate controls (water) and positive-template controls.

Results: From July 2009 to December 2013, 7,626 samples have been tested, and a total of 2,152 (28.2%) were positive for influenza A virus. Subtype A (H1N1)pdm 2009 was predominantly detected in 1,631 (75.7%) of samples.

Positive results were higher among adults: 45.9% of patients positive for influenza A (H1N1)pdm 2009 were from 15 to 49 years old and 8.4% of them were from 50 to 65. Only 2.9% were older than 65. Children younger than 5 years corresponded to 18.8% of positive samples and from 6 to 15 years old contributed with 24% of them. Almost half of these tests were performed during the 2009 pandemic: 3,544 samples were tested during that year, with 1,244 (35,1%) positive for influenza A virus, 89.0% of them for subtype A (H1N1)pdm 2009.

Subsequent years have shown decreased spontaneous demand for the test, as well as less intense circulation of pandemic viral subtype: 715 samples analyzed in 2010, 340 in 2011 and 883 in 2012, with a positivity rate for influenza A (H1N1)pdm 2009 of 4.6%, 7.3% and 8.0%, respectively.

However, an important increase in this demand was registered in 2013, when 2,116 samples were analyzed. It is worthy to notice that, not only the positivity rate (18.7%) increased comparing to former years, but subtype A (H1N1)pdm 2009 became predominant again. While in 2010, 2011 and 2012 it corresponded to, respectively, 47.8%, 29.1% and 27.4% of positive samples for influenza A virus, in 2013 this proportion was 88.9%, very similar to what had been seen during the pandemic.

Discussion and Conclusions: Influenza A (H1N1)pdm 2009 virus has been a persistent cause of respiratory infection in Brazil since its introduction during the pandemic. In 2009, most cases occurred in adults, but the elderly corresponded to a small proportion. It has been hypothesized that previous immunization or infection with other viral strains, including in former epidemics of H1N1 subtype, might have played a role partially protecting these individuals.

In Brazil, citizens over 60 years are routinely vaccinated by the Public Health system in yearly campaigns during the autumn. After the pandemics, Brazilian population was largely immunized during autumn 2010, although the vaccine had not been available for all citizens in Public Health system, which provided it for free only for children under 2 years old, elderly over 60 years old, pregnant women, people with comorbidities or any kind of immunosuppression, native Brazilians and other special groups. However, the alarm due to the recent pandemic stimulated the search for vaccines in private facilities by persons who did not have this right guaranteed by the government.

This probably contributed not only for decreasing the number of infections and the demand for the test, but to diminished A (H1N1)pdm 2009 subtype circulation, since it represented less than one third of influenza A infections in our sample in 2011 and 2012. However, probably due to Brazilian strategy for influenza immunization, which is not universal in Public Health system, a recrudescence of A (H1N1)pdm 2009 subtype has been documented. People who had been immunized in 2010 and had not received any other dose in the following years probably had lower antibody titers, which made them susceptible to new infections, considering the virus may have accumulated drift mutations during this period. The number of infections detected increased, which is consistent with national statistics that also reported an increase in the number of severe cases, particularly on the Southeast area of the country, where most of our samples come from.

We concluded that influenza A (H1N1)pdm 2009 is still a public health problem in Brazil, which should motivate new prevention strategies supported by the Ministry of Health, surely considering universal immunization, and also improving surveillance and the availability of diagnostics.