Jul 23, 2010 (CIDRAP News) – The global H5N1 avian influenza situation has not improved very much since the virus began spreading widely in 2003, and many human cases have probably gone unreported, French health experts conclude in an assessment published yesterday in Eurosurveillance.
While the deadly virus still has not gained the ability to spread easily from person to person, "The overall worldwide situation of influenza A(H5N1) . . . is not markedly improved since 2003," says the report by researchers from the French Institute for Public Health Surveillance (Institut de Veille Sanitaire) in Saint-Maurice, a French government agency.
"This fact, and regular reintroduction of the virus by wild birds in countries where foci have been controlled (such as Bulgaria, Romania, Turkey or Vietnam) underscore the importance of maintaining adequate surveillance and response capacities for infections in both animals and humans," the authors add.
They also write that the World Health Organization's (WHO's) human H5N1 case count "probably vastly underrepresents the true case burden worldwide." The count reached 501 cases, including 297 deaths, yesterday.
In Indonesia, they say, the case-fatality rate (CFR) for H5N1 is 88%, and nearly all the cases identified since January 2009 have been on the island of Java, which suggests that access to diagnosis is uneven and that severe cases are overrepresented in the official count.
The CFR is lower in Egypt, probably reflecting better access to timely diagnosis and care, the report adds, "but suspected human cases occurring in remote locations may not all be officially detected and/or reported and would have contributed to a higher CFR."
Reviewing the H5N1 situation in birds, the authors note that 63 countries and territories in Asia, Africa, and Europe have had outbreaks in poultry and/or wild birds since the end of 2003. Twelve countries have had poultry outbreaks so far this year: Bangladesh, Bhutan, Cambodia, Egypt, India, Indonesia, Israel, Laos, Myanmar, Nepal, Romania, and Vietnam.
"Many other countries, notably in sub-Saharan Africa, have suspected transmission in predominantly backyard flocks but lack surveillance systems to document it," the article says.
Discussing the patterns of human cases, the report observes that the numbers have generally trended downward over the past 6 years and that most cases have occurred in the months from November to April, though Indonesia has cases throughout the year. In recent years the number of cases has fallen in Asia and grown in the Near East, mainly Egypt. The latter accounted for 66 of 149 cases (44%) from Jan 1, 2008, to Jul 1, 2010.
At least 40 clusters of human cases, accounting for more than 100 illnesses in all, have occurred since 2003, the researchers report. Common exposure to sick poultry was the source of infection in the vast majority of these, but investigators concluded that limited human-to-human transmission occurred in some of the clusters, most of which were in families.
Genetic susceptibility probably has played some role in the clusters, as suggested by the three-generation cluster in Indonesia in 2006 and by clusters in Turkey, the report says. It adds that no instances of transmission in healthcare settings have been confirmed since 2003.
In conclusion, the experts say that some countries that were hit hard by H5N1 before 2007, such as Thailand and Turkey, seem to have controlled the problem and reduced risks to humans. But the virus continues to circulate in poultry elsewhere, especially Egypt, Indonesia, and Bangladesh.
While Egypt and Indonesia face a complex situation, "communication in these countries is transparent and constructive and allows for quick reporting of cases, especially if suspected clusters should arise," the article says. It notes that Indonesia authorities last December resumed the practice of reporting cases to the WHO. In June 2008 the Indonesian health minister had said the government would no longer report cases as they occurred and instead would give only periodic updates.
The virus still has the potential to spark a human pandemic, the researchers state. Unlike in 2003 and 2004, poultry outbreaks and human cases now are occurring in some of the most densely populated areas in the world, which may increase the risk of transmission from birds to humans and make it harder to contain the virus if it starts spreading among humans, the experts assert.
Tarantola A, Barboza P, Gauthier V, et al. The influenza A(H5N1) epidemic at six and a half years: 500 notified human cases and more to come. Eurosurveillance 2010 Jul 22;15(29) [Full text]