[Source: World Health Organization, full PDF document: (LINK). Edited.]

Influenza Update N 191, 02 August 2013

  • Influenza activity in the northern hemisphere temperate zones remained at inter-seasonal levels. The United States of America reported 14 cases of human infection with influenza A(H3N2)v so far this year, since the first case in June. More details can be found at http://www.cdc.gov/flu/swineflu/h3n2v-cases.htm.
  • In most regions of tropical Asia influenza activity decreased, except for Cambodia, India and Viet Nam where there are some signs of increasing influenza A activity. In Central America and the Caribbean regions, influenza activity continued to increase in Costa Rica, El Salvador and Nicaragua, remained high in Cuba, and decreased in the Dominican Republic. In tropical South America, influenza A(H1N1)pmd09 became the predominant circulating virus in most countries, except in Ecuador where respiratory syncytial virus (RSV) remained the most commonly detected respiratory virus.
  • Influenza transmission has peaked in the southern cone of South America and in South Africa in late June. In all of those areas, transmission was primarily associated with influenza A(H1N1)pdm09. In Australia and New Zealand, numbers of influenza viruses detected and rates of influenza-like illness have been lower than in previous years, but have not yet definitively peaked. Influenza A(H3N2) and type B have been much more commonly detected than A(H1N1)pdm09 in both of those countries.
  • As of 23 July, a total of 134 cases of influenza A(H7N9) virus infection have been reported. For more details see: http://who.int/influenza/human_animal_interface/influenza_h7n9/en/index.html

Countries in the temperate zone of the northern hemisphere

North America

Overall influenza activity in North America remained at low levels throughout most of the region.

In Canada, influenza activity remained at inter-seasonal levels.

In the United States of America (USA), influenza activity remained low and at inter-seasonal levels. The USA has reported 14 human infections with influenza A(H3N2)v virus in 2013 since the first case in June. For more details see http://www.cdc.gov/flu/swineflu/h3n2v-cases.htm.


Influenza activity in Europe remained at inter-seasonal levels. Consultation rates for ILI and ARI were at low levels for all countries in the region.

None of the specimens collected from sentinel sites tested positive for influenza.

Northern Africa and the Western Asia region

Influenza activity is low in the Northern Africa and western Asia. Influenza A(H1N1)pdm09 has been detected throughout the season in most countries in western Asia, with the exception of Jordan which reported a majority of influenza B.

Northern Asia

Influenza activity in the temperate region of Asia has been at inter-seasonal levels since late May.

As of 23 July 2013, 134 cases of influenza A(H7N9) have been identified, of which 43 have died. This represents on additional case since the last update. more and updated information is posted at: http://who.int/influenza/human_animal_interface/influenza_h7n9/en/index.html


Countries in the tropical zone

Tropical countries of the Americas/Central America and the Caribbean

Influenza activity in Caribbean and Central America continued to increase in Costa Rica, El Salvador and Nicaragua, remained high in Cuba, and decreased in the Dominican Republic. Co-circulation of influenza A(H1N1)pmd09 and A(H3N2) was reported in the region.

Influenza activity in Costa Rica and El Salvador continued to increase with influenza A(H1N1)pmd09 being the most commonly detected influenza virus.

Nicaragua also reported a sharp increase in the percentage of positive samples, with 15.6% testing positive in mid-June and 41.1% testing positive in the most recent week. Among the 30% of samples that tested positive for influenza, two thirds were influenza A(H3N2) and one-third influenza A(H1N1)pmd09.

Influenza activity remained high in Cuba, but has decreased since mid-June. Of 589 specimens tested, 33.3% tested positive for influenza viruses. Of those that were positive for influenza A, 73.5% were influenza A(H1N1)pmd09 and 26.5% were influenza A(H3N2). Rhinovirus and para-influenza also continued to circulate in Cuba.

Influenza activity also began to decrease in the Dominican Republic. Out of 157 samples tested, the proportion testing positive for influenza decreased from 45.9% in mid-June to 29.6% in the most current week, with influenza A (not subtyped) being the most detected virus.

In tropical South America, influenza transmission is generally low, but influenza A(H1N1)pmd09 remained the most commonly detected respiratory virus in the region.


Central African tropical region

Many countries in the Central African tropical region reported low or no influenza activity. Cote dIvoire reported higher activity of influenza B, whereas in Cameroon, there was higher activity of A(H1N1)pdm09. After peaking at the end of May, influenza activity in Madagascar continued to decrease.


Tropical Asia

Influenza transmission in southern Asia and South East Asia remained consistently low for most countries except for Cambodia, Thailand and Viet Nam. All reported more influenza A(H3N2) virus detections than influenza A(H1N1)pdm09.


Countries in the temperate zone of the southern hemisphere

Temperate countries of South America

In temperate South America, influenza virus transmission has continued to decrease since peaking in June and has primarily been associated with influenza A(H1N1)pdm09.

In Argentina, the number of ILI cases were higher throughout the season than average for the previous 5 years. However, SARI hospitalizations were similar to previous years; both have been decreasing. Of the 1408 samples analyzed in early July, 22% were positive for influenza. Among samples positive for influenza viruses, the large majority have been influenza A(H1N1)pdm09 with smaller numbers of A(H3N2).

In Chile, the national ILI consultation rate began to show a significant decline compared to the previous week. RSV remained the most common virus detected. Among the 2065 samples collected, 8.5% were positive for influenza viruses. Among the positive specimens, the large majority have been influenza A(H1N1)pdm09 with smaller numbers of A(H3N2) and influenza type B.

In Uruguay, the proportions of SARI hospitalizations and SARI-related ICU admissions appears to have recently peaked. In the two weeks of mid-July, 19% of specimens collected from SARI patients were positive for influenza viruses. Of those, the large majority were associated with influenza A(H1N1)pdm09


Temperate countries of Southern Africa

Influenza activity in South Africa has continued to decrease since the peak of the season in early June. Specimens collected from sentinel sites indicate that Influenza A(H1N1)pmd09 remained the most commonly detected influenza subtype, although small numbers of influenza A(H3) and influenza B have also been reported.


Oceania, Melanesia and Polynesia

Australia, New Zealand and the Pacific Islands continued to report low influenza and ILI activity. During the week ending 7 July 2013 in Australia, the ILI consultation rate remained stable and was still slightly lower than the usual rate for this time of year. In New Zealand, during 15 to 21 July 2013, influenza activity continued to remain below the baseline threshold, but with increasing trends. Seventy-three out of 260 samples received were positive for influenza: 35 were influenza B, 15 were influenza A(H3N2), 9 were influenza A(H1N1)pdm09 and 14 influenza A (not subtyped).


Source of data

The Global Influenza Programme monitors influenza activity worldwide and publishes an update every two weeks.

The updates are based on available epidemiological and virological data sources, including FluNet (reported by the Global Influenza Surveillance and Response System) and influenza reports from WHO Regional Offices and Member States. Completeness can vary among updates due to availability and quality of data available at the time when the update is developed.

Link to web pages-