21 October 2011
Update number 145
- Countries in the temperate zone of the northern hemisphere
- Countries in the tropical zone
- Countries in the temperate zone of the southern hemisphere
- From the peer-reviewed literature
- Virological surveillance
Please note, in the interest of standardization and clarity, WHO has now adopted new standard nomenclature for the 2009 influenza A(H1N1) pandemic virus following the recommendations of a recent WHO Consultation on the Composition of Influenza Vaccines. In this and future publications, the nomenclature used will be: influenza A(H1N1)pdm09.This will replace the previously used influenza A(H1N1)2009 and H1N1(2009). See the Weekly Epidemiological Record (WER), 21 October 2011, vol. 86, 43 (pp 469–480)
• Influenza activity in the temperate regions of the northern hemisphere remains low or undetectable.
• Influenza activity the tropical zone is active in a few countries of the Americas (Cuba, Honduras and El Salvador), central Africa (Cameroon), and Southern and Southeast Asia (Bangladesh, Cambodia, Thailand, Lao People's Democratic Republic and Viet Nam.
• Transmission in South Africa and South America remains low and the season appears largely over.
• Influenza activity has peaked in Australia and New Zealand, though there are regional variations in the timing of the peaks and the season has not yet finished. Australia continues to see regional differences in the predominant virus subtype.
The countries in the northern hemisphere temperate zone are still in their inter-seasonal period for influenza. Many of the countries suspend surveillance activities during the summer months and have now resumed influenza monitoring at the start of October but none report a start of active community transmission of influenza.
In the tropical countries of Americas, generally low levels of influenza transmission are reported. In the Dominican Republic, influenza transmission is reported to be sustained at a low level, with influenza type B now the most common influenza virus detected. Influenza virus detections in Cuba, Honduras and El Salvador appear to have peaked in mid to late September, with influenza A(H3N2) as the predominant strain. In Panama, influenza A(H1N1)pdm09 has been consistently the predominant virus detected since late June. Other Central American countries reported no or very low influenza activity. Countries of the tropical area of South America have reported low or undetectable levels of influenza transmission. The previously reported transmission of predominantly influenza A(H1N1)pdm09 in Bolivia has now returned to baseline level, after its peak in mid September.
In sub-Saharan Africa, influenza transmission has continued in Cameroon, primarily influenza B with smaller amounts of influenza A(H1N1)pdm09 and increasing numbers of influenza A(H3N2) in recent weeks, and peaking in week 38. In eastern Africa, continuous low level transmission of a mixture of influenza type B, A(H3N2), and A(H1N1)pdm09 since the peak of transmission in March is reported.
Influenza transmission in tropical Asia has continued to be active in localized areas. Transmission of primarily influenza B was reported in India, Bangladesh and Cambodia, though in India it has now returned to low levels. Circulation of influenza A(H3N2) persist in Thailand and Lao People's Democratic Republic after their peaks in early and late September, respectively. Viet Nam also report sustained transmission of predominantly influenza A(H1N1)pdm09 which has been continuous since the beginning of 2011.
Influenza activity has continued to decline in the temperate regions of South America and are approaching baseline, intra-seasonal levels. Co-circulation of influenza type A(H3N2) and A(H1N1)pdm09 persist in Argentina and Chile, though a large proportion of viruses there are not subtyped, while influenza A(H3N2) is predominant in Paraguay. The overall severity of influenza of this season in Argentina and Chile has been similar to that observed during previous seasons, with regard to numbers of influenza-like illness (ILI) (Chile and Argentina), percentages of respiratory admissions in children younger than 5 years (Chile), and the numbers of pneumonia cases (Argentina). In Uruguay, the proportion of severe acute respiratory infection (SARI) hospitalizations, ICU admissions and deaths remained <5% in the first week of October, a rate which is comparable to the same period in the 2010 season. In Paraguay, the proportion of ILI consultations decreased to 6% and the proportion of SARI hospitalizations, ICU admissions and deaths remained below 10% in the last week of September.
Influenza transmission in South Africa has continued at low level since peaking in early June.
Australia, New Zealand and South Pacific
The influenza season is still ongoing in Australia and New Zealand, though activity is declining. ILI consultation rates have started to decline nationally in Australia. In the week ending 2 October 2011, the national ILI consultation rate to sentinel general practioners was 9 cases per 1000 consultations, down from 12 cases per 1000 in the previous report. Respiratory illness presentations to Western Australia Emergency Departments decreased compared to the previous fortnight, though they remained well above baseline levels. ILI presentations to New South Wales Emergency Departments were similar to the previous week, and activity was reported as being below the usual range for this time of year. 58% of ILI presentations occurred in people aged 25 to 44 and 55-64. Total admissions from New South Wales Emergency Departments to critical care units for ILI and pneumonia decreased this week, and remained within the usual range for this time of year.
Up to 30 September, there have been 24 049 laboratory confirmed notifications of influenza diagnosed during 2011. Nationally, weekly notifications for this season have peaked in early August, though the timing of the peaks varied between different regions. This number exceeds that reported in previous years other than the 2009 pandemic year.
The Influenza Complications Alert Network Sentinel Hospital System in Victoria, South Australia, Western Australia and the Australia Capitol Territory has reported 223 hospitalizations including 31 ICU admissions associated with influenza from 1 May 2011 to 30 September. Almost half of the hospitalizations and 45% of ICU admissions have been associated with influenza A(H1N1)2009 infection. The mean age of patients hospitalized has been 51 years.
The majority of states and territories have reported mostly influenza A(H1N1)pdm09 with co-circulation of influenza B. However, in the Northern Territory this fortnight notifications of influenza A(H3N2) represent 70% of their notifications, and nationally the majority of A(H3N2) notifications are being reported from the Northern Territory, Queensland and Western Australia. In Tasmania and New South Wales influenza B represents around half of their notifications, and the proportion of influenza B in Queensland appears to be increasing.
In New Zealand, the rate of national ILI consultations has decreased to 29.0 per 100 000 (108 ILI consultations), which is below the baseline rate of 50 per 100 000 consultations. Influenza type A(H3N2), A(H1N1)pdm09 and B viruses co-circulate in the population.
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.