07 October 2011
Update number 144
- 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
• Influenza activity in the temperate regions of the northern hemisphere remains low or undetectable.
• Countries in the tropical zone mostly reported low influenza activity but with some transmission reported in countries of the Americas (Cuba, Honduras and Bolivia), western Africa (Cameroon), and southern Asia (India, Thailand, Viet Nam and Singapore).
• Transmission in South Africa and South America remains low.
• As reported in previous update, the number of laboratory confirmed influenza notifications in Australia is reported to be declining in Queensland, New South Wales and other states with the exception of the Northern Territory. Influenza-like illness (ILI) activity in New Zealand continues around national baseline levels and the majority of viruses detected have been influenza B.
The countries in the northern hemisphere temperate zone are in their inter-seasonal period for influenza. All of the countries in this zone reported low or no influenza activity.
In the tropical countries of the Americas, generally low levels of influenza transmission are reported; Cuba has experienced an increase in influenza A(H3N2), while the previously noted circulation of influenza A(H1N1)pdm09* in the Dominican Republic has decreased to very low levels. Honduras has had recent circulation of influenza A(H3N2), which peaked in mid August. Influenza A(H3N2) circulation in El Salvador began in mid-August and has been increasing weekly. Most countries of the tropical area of South America reported low or undetectable levels of influenza transmission. The previously reported influenza transmission in Colombia (primarily A(H1N1)pdm09 with lower numbers of H3N2) and Brazil (roughly equal numbers of A(H1N1)pdm09, H3N2, with lower numbers of influenza type B) now have returned to very low levels. However, Bolivia has reported a recent increase in transmission of influenza A(H1N1)pdm09 after a earlier wave of influenza A(H3N2) in May-June mainly in La Paz.
In sub-Saharan Africa, some influenza transmission has continued in the west, notably in Cameroon where transmission has primarily been influenza B with increasing numbers of influenza A(H1N1)pdm09 in recent weeks, peaking in week 36. In eastern Africa, continuous 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 been active in localized areas. Moderate transmission of primarily influenza A(H3N2) was recently reported in India, Singapore and Thailand, though transmission in India has now returned to low levels. Influenza A(H3N2) circulation in India and Bangladesh was largely replaced by influenza type B in the recent weeks. Circulation of influenza A(H3N2) in Thailand, which began two to three weeks later than the other countries, has continued at a relatively high level, though it appears to have recently peaked. Lao People's Democratic Republic has also reported predominant transmission of influenza A(H3N2) in recent weeks, increasing markedly in early September. In contrast, Viet Nam and Cambodia report sustained transmission of predominantly influenza A(H1N1)pdm09.
Low levels of influenza activity are now reported in the temperate regions of South America, where the influenza activity is declining back to baseline levels. In Chile, influenza A(H1N1)pdm09 detections were substantially lower than the past four weeks, ILI activity and consultations for respiratory disease in emergency departments also remained at low levels; three deaths from influenza A(H1N1)pdm09 were reported in week 37, two of which had co-morbidities. Transmission is similar in Argentina, where influenza A(H3N2) has been the most common virus circulation. The country has reported low and decreasing levels of ILI and severe acute respiratory illness (SARI) activity and fewer samples testing positive for influenza into week 38. In Paraguay, the proportion of SARI hospitalizations, SARI intensive care unit (ICU) admissions, and SARI related deaths were below 5%, all either similar to or decreased from recent weeks; in the samples tested, no influenza virus was detected. In Uruguay the proportions of SARI hospitalizations and SARI deaths continues to decline below five percent; the proportion of SARI ICU admissions also continued to decrease (5%) after peaking in week 31.
Influenza transmission in South Africa has continued at low levels after two peaks in week 23 and week 34. The influenza season was dominated by influenza A(H1N1)pdm09 with smaller numbers of influenza type B and some influenza A(H3N2).
Australia, New Zealand and South Pacific
Influenza transmission rates have remained consistent through week 39 in Australia, although the weekly number of laboratory confirmed influenza notifications has continued to decline in Queensland, New South Wales (NSW) and most other states except the Northern Territory. Overall the peak of influenza notifications seems to have been in early August, which was above the peak frequency experienced in previous years except 2009.
The majority of states and territories have reported mostly influenza A(H1N1)pdm09 with co-circulation of influenza B; except in Tasmania and NSW where influenza B predominates, and Western Australia reporting a mix of influenza A(H1N1)pdm09, A(H3N2) and very little influenza B. From 1 May to 22 September, there were 155 influenza hospitalizations (including 20 ICU admissions) in Victoria, South Australia, Western Australia and the Australia Capital Territory. About 53% of the hospitalizations and 60% of the ICU admissions were associated with influenza A(H1N1)2009; mean age of the hospitalized patients was 49 years.
In New Zealand, the rate of national ILI consultations was 30.7 per 100 000. Influenza type A(H3N2) virus and type B account for a large proportion of influenza viruses detected in New Zealand. In the Pacific Islands ILI activity has been variable with increased activity in Fiji, Solomon Islands, Marshall Islands, and Northern Mariana Islands.
*previously referred to as A(H1N1)2009.
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.