Influenza update - 01 July 2011
Update number 137
- 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 is at baseline inter-seasonal levels.
• Transmission in tropical areas is low overall with focal areas of transmission noted in a few countries of Central America and northern South America, western and eastern regions of sub-Saharan Africa, and tropical Asia.
• The influenza season has now started in South Africa and may be starting in Australia as well. South Africa has continued to report increasing numbers of both mild and severe cases, primarily related to influenza A(H1N1)2009. Australia has noted a recent increase in emergency room visits due to influenza-like illness and significantly increased notifications of influenza activity in the states of South Australia and Queensland.
The influenza season in the northern hemisphere temperate areas has largely ended. In Canada, only two regions reported sporadic activity in the past week and influenza virus detection was very low. In the United States of America (USA), two pediatric deaths associated with influenza A(H3N2) virus and influenza type B virus were reported, however, rates of influenza-like illness (ILI) are below the seasonal threshold. Only two of the clinical specimens tested in Mexico in the past week were found to be positive to influenza. Influenza activity in Europe, northern Africa, and north Asia remained at low levels or none at all.
Overall, influenza activity in tropical zones remains low with some focal areas of transmission. The Central America region has reported low or no influenza activity for most countries. The previously noted transmission of influenza A(H1N1)2009 in the Dominican Republic has increased over the past three weeks, while Honduras and El Salvador reported low levels of influenza type B transmission. In tropical South America, Colombia has detected low level circulation of both influenza A(H3N2) and influenza A(H1N1)2009, with the latter slightly more common. Respiratory syncytial virus is also reported in Colombia, though numbers are decreasing. The most common virus detected in patients admitted to hospital with respiratory disease in Colombia was influenza type A. Bolivia has reported increasing numbers of influenza A(H3N2) detections for the past eight weeks and currently about 20% of clinical specimens tested are positive for the virus.
Transmission of influenza type B has been noted in West Africa. Mali, Ghana, Togo, Nigeria and Cameroon all report moderate numbers of positive influenza test results with influenza B. Ghana has also reported smaller numbers of influenza A(H1N1)2009 and influenza A(H3N2). The number of laboratory-confirmed cases has increased since the last update in the area. In East Africa, transmission has decreased to low levels in recent weeks as reported by Rwanda, Uganda and Kenya. A mix of viruses was seen in East Africa in recent weeks with Kenya and Uganda reporting primarily H1N1 (2009) and influenza type B, while in Rwanda nearly all of the viruses detected have been H3N2.
Overall, influenza activity in the tropical countries of Asian continues to remain low. Sporadic activity has been reported in Sri Lanka, Indonesia, southern part of China (including Hong Kong Special Administrative Region), Singapore, Viet Nam, and Cambodia. Viral distribution of these countries remains similar since the last update, with a mixture of H1N1 (2009) and influenza type B. In India, small numbers of H3N2 have been persistently detected over the last 3 weeks after many weeks of no virus detection.
Influenza transmission remains low in the temperature regions of South America. In Chile, ILI rates have increased slightly while severe acute respiratory infection (SARI) rates have remained stable and at low levels. Although influenza A(H1N1)2009 was the most commonly detected influenza virus in Chile and Argentina, numbers of viruses detected are very low. Uruguay reported sporadic cases of influenza B and H1N1 (2009).
The National Institute for Communicable Diseases of South Africa has reported that influenza activity remains high. More than 80% of the influenza viruses recovered from SARI cases in the last two weeks have been influenza A(H1N1)2009. Influenza type B, has also been detected in small but increasing numbers of cases. Only a few influenza A(H3N2) have been reported.
Australia and New Zealand and South Pacific
Influenza activity in both Australia and New Zealand remains low. However, Australia noted a recent increase in emergency room visits due to ILI. In addition, notifications of influenza activity have risen significantly in the states of South Australia and Queensland, with some increases also observed in other areas. Overall, the viruses detected were mostly identified as influenza A(H1N1)2009 with lower number of cases of influenza type B and H3N2, however, in South Australia, 85% of viruses detected were influenza B with no H3N2. National ILI consultation rate from New Zealand remains below baseline activity. Influenza type B remains the most common virus detected there, though influenza A(H1N1)2009 has been detected sporadically in the past few weeks.
Three recently published studies investigated the effects of maternal influenza infection and vaccination on pregnancy outcomes and newborn respiratory disease.
One study from the United Kingdom compared the rates of stillbirth, perinatal mortality, and neonatal mortality between a prospectively identified cohort of pregnant women who were admitted to the hospital with confirmed influenza A(H1N1)2009 infection and a historical cohort of pregnant women admitted to hospital in 2005 and 2006. This study found that perinatal mortality was significantly higher in influenza-infected women compared to the historical cohort (39 deaths/1000 live births vs. 9 deaths/1000 live births respectively, p<0.001) as was the likelihood of premature birth. (Pierce P et al. Perinatal outcomes after maternal 2009/H1N1 infection: national cohort study, BMJ 2011; 342:1351-1358.)
A second study from the USA evaluated the impact of influenza vaccination of pregnant mothers. This study followed a cohort of pregnant women who gave birth to 4,326 live infants between June 2004 and September 2006. The study looked at rates of prematurity in infants born during the influenza season (October - May) and found that pregnant mothers who received influenza vaccination were 72% less likely than unvaccinated women to deliver prematurely during the period of most widespread influenza activity (adjusted OR = 0.28; 95% CI, 0.11–0.74). The odds of prematurity during the period between influenza seasons was similar between the two groups. (Omer SB et al. Maternal influenza immunization and reduced likelihood of prematurity and small for gestational age births: a retrospective cohort study, PLoS Med 2011; 8:e1000441.)
In the third study, also from the USA, Poehling et al. evaluated influenza-associated hospitalizations of infants from three geographically diverse counties in the USA where population based hospital surveillance has been carried out for several years. They found that infants of vaccinated mothers are 45-48% less likely to be hospitalized for influenza infection than those of unvaccinated mothers in the first six months after birth (adjusted odds ratio, 0.52; 95% confidence interval, 0.30–0.91). (Poehling KA et al. Impact of maternal immunization on influenza hospitalizations in infants, Am J Obstet Gynecol 2011; S141-148.)
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 Network) 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.