23 September 2011
Update number 143
- 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, Vietnam and Singapore).
• Transmission in South Africa has declined to low levels. In Australia, the number of laboratory confirmed influenza notifications is reported to be declining in Queensland, New South Wales (NSW) and other states with the exception of the Northern Territory. Oseltamivir-resistant (but sensitive to zanamivir) influenza A(H1N1)2009 was identified in a cluster of cases in the Newcastle region of New South Wales; no travel history was found among the cases, and none have died. 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. Nearly all of the countries in this zone reported low or no influenza activity.
In Central and tropical South America, generally low levels of influenza transmission are reported; RSV continues to be the predominant virus in Central America and the Caribbean since week 24. Cuba reports low level of circulation of influenza A(H3N2) since week 29. Honduras has had recent circulation of influenza A(H3N2), which peaked in mid August. The H3N2 circulation there was associated with smaller amounts of influenza A(H1N1)2009 and type B. Bolivia has reported sporadic detections of influenza A(H1N1)2009 and influenza A(H3N2). The previously reported influenza transmission in Colombia (H1N1 with smaller numbers of H3N2) and Brazil (roughly equal numbers of H1N1, H3N2, and type B) has largely finished.
In sub-Saharan Africa, some influenza transmission has continued in the west, notably in Cameroon where transmission has been predominantly influenza type B with smaller but increasing numbers of influenza A(H1N1)2009 in the last weeks. In eastern Africa, continuous transmission of a mixture of influenza type B, A(H3N2), and A(H1N1)2009 since the peak of transmission in March are reported. Transmission in Kenya has decreased with fewer positive samples for influenza in recent weeks, which have been a mixture of influenza B, A(H3N2), and A(H1N1)2009.
Influenza activity in most of tropical Asia has been active in localized areas. Moderate transmission of primarily influenza A(H3N2) was reported in India, Bangladesh, Singapore and Thailand, though transmission in India has now peaked and returned to low levels. Small numbers of influenza type B and H1N1(2009) have also been reported from those countries. In contrast, Viet Nam continues to report sustained transmission of predominantly influenza A(H1N1)2009 since the beginning of 2011, which reached higher levels in mid August. Twenty seven percent of severe viral pneumonias reported to Viet Nam's sentinel surveillance system have been positive for influenza, 96% of those influenza A(H1N1)2009. Lao People's Democratic Republic has predominant transmission of influenza A(H3N2), though at low levels. Cambodia reports a slight increase in the number of specimens positive for influenza A(H1N1)2009 and influenza type B. In Singapore influenza-like illness (ILI) made up only 1% of polyclinic attendances for acute respiratory illness, which is considered low. Influenza A(H3N2) constituted 69% of all the influenza virus specimens collected in August 2011 followed by influenza type B at 20% and influenza A(H1N1)2009 at 6%.
Lower levels of influenza activity were reported in the temperate regions of South America, where the season appears to have peaked and is declining. In Chile, influenza A(H1N1)2009 detections were substantially lower than the past four weeks, ILI activity and consultations for respiratory disease in emergency departments also remained at low levels; ten deaths from influenza A(H1N1)2009 were reported in week 35, nine of which had co-morbidities. The situation in Argentina is similar with low and decreasing levels of ILI and severe acute respiratory infection (SARI) activity and fewer samples testing positive for influenza, with co-circulation of influenza A(H1N1) 2009 and influenza A(H3N2) among the subtyped influenza A viruses. In Paraguay, the proportion of ILI consultations was slightly higher than the previous week (~9%) and the proportion of SARI hospitalizations, SARI 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 since peaking in early June. The influenza season was dominated by influenza A(H1N1)2009 with smaller numbers of influenza type B and some influenza A(H3N2). Notably, South Africa experienced a secondary peak of influenza in late August primarily associated with influenza A(H3N2) and B.
Australia, New Zealand and South Pacific
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; but in many states these notifications are still above the peak levels observed in 2010.
Two additional cases of oseltamivir resistant influenza A(H1N1)2009 have been reported in NSW associated with the previously reported cluster of cases in that state. These new cases have no prior travel history to the originally affected region of the state; all of the viruses from the cluster were found to be sensitive to zanamivir and without any antigenic changes that would have affected their recognition by vaccine-induced antibodies. (see the Influenza Update from two weeks ago for more details about this cluster). This represents a wider area of spread of this cluster of viruses though the numbers appear to be declining as the season in Australia wanes.
The majority of states and territories have reported mostly influenza A(H1N1)2009 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)2009, A(H3N2) and very little influenza B. By 2 September 2011, the National Notifiable Diseases Surveillance System (NNDSS) had reported 19,987 confirmed cases of influenza of which the peak this season was in the week ending 5 August, with 1,952 cases. From 1 May to 1 September, there were 118 influenza hospitalizations (13 ICU admissions) in Victoria, South Australia, Western Australia and the Australia Capital Territory. About 56% of the hospitalizations and 77% of the ICU admissions were associated with influenza A(H1N1)2009; mean age of the hospitalized patients was 46.6 years.
In New Zealand, the rate of national ILI consultations was 50.7 per 100 000, and is at or above baseline levels but has not reached high levels in this season. Influenza type B virus accounts for a large proportion of influenza viruses detected in New Zealand. In the Pacific Islands, most countries reported low influenza activity, with the exception of Samoa, Fiji, Solomon Islands, Marshall Islands, Tonga and Kiribati.
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.