This post wraps the latest debate about the impact of pandemic influenza in Australia, and includes an article from public health physician, Dr Craig Dalton (how bad was the pandemic really, he asks), PLUS a stack of links to recent international publications (these are at the very bottom).
In the letters pages of the latest Medical Journal of Australia, intensive care doctors from four hospitals have raised concerns about a previous MJA article, which concluded that “the clinical course and outcomes of pandemic (H1N1) 2009 influenza virus are comparable to those of the current circulating seasonal influenza”, and that “the high number of hospital admissions reflects a high incidence of disease in the community rather than an enhanced virulence of the novel pandemic influenza virus”.
The intensive care doctors are “concerned that these assertions underemphasise the true severity of the influenza pandemic, and have led to inappropriate reporting in the media”.
The authors of the original article responded, saying that the large numbers of intensive care admissions for pandemic flu are “not a function of enhanced virulence of the pandemic strain, but rather a function of vast numbers of infected individuals in a naïve population”. They also cite an article by the Australian and New Zealand Intensive Care Study investigators in support of their conclusions, noting that this group also found no difference in outcome between pandemic (H1N1) 2009 and seasonal influenza.
Meanwhile, Craig Dalton and other NSW colleagues reported the results of their investigations into whether patients with pandemic flu were more likely to end up in intensive care than those with seasonal influenza A infection. Based on state-wide data, they calculate a relative risk of 4.9 (95% CI, 3.5–7.0) for admission to ICU with pandemic (H1N1) 2009 influenza compared with seasonal influenza A infection.
Also in the journal, Dr Peter Collignon, Director of the Infectious Diseases Unit and Microbiology Department at Canberra Hospital, suggests that most of the mortality predictions for this epidemic have been consistently wrong and exaggerated. Together with predictions of second and third killer waves, these have generated needless fear and inappropriate responses, he says.
Craig Dalton has provided this overview below for Croakey readers. He writes:
“Was it a beat up or a near miss? Controversy continues but we now have most of the pieces of the puzzle to answer this question.
It was, as health authority sound bites so clearly stated: “mild in most, severe in some”. There were concerns in Mexico in early March about a nasty respiratory outbreak that was thought to be due to seasonal influenza, but it wasn’t until two children in California were identified with a new flu strain by a molecular fingerprinting study that pandemic alarm bells were rung.
The pandemic virus hit Australia before the usual influenza season. Many general practitioners and emergency departments were swamped with pandemic influenza patients or those that feared they had pandemic influenza. This gave an initial impression of high influenza attack rates in affected communities.
However, our own Flutracking.net influenza surveillance, Google Flu Trends and work absenteeism surveillance suggested influenza-like illness rates were no higher than previous years and the rates were lower than in 2007. Importantly influenza related mortality was no different in the general community and from an anecdotal perspective – just looking at the low rates of illness among work colleagues, family and friends – it just didn’t feel like a “bad flu year”. However, it was a different story in hospital wards and intensive care units.
Because most of the pandemic related disease was mild it took some 4 to 6 weeks before we saw severe cases of pandemic influenza began to mount. Between June and August Intensive care units steadily admitted more and more patients with severe lung disease due to pandemic influenza. The Australian New Zealand Intensive Care (ANZIC) study found that obesity, pregnancy, asthma and other chronic lung conditions, diabetes, and Indigenous status were associated with increased risk of admission to ICU and the age of admissions were younger than patients typically admitted to ICU with seasonal influenza. The study also found that 32% of the patients had no underlying risk factor to explain the severity of their influenza infection. While pandemic patients were young, the median age of all cases was the twenties, for hospitalisation it was the thirties, for ICU admission the forties and for deaths the fifties – each decade seemed to move patients to a need for higher care or towards a fatal outcome.
Controversy rages in this week’s edition of the Medical Journal of Australia where three letters debate the seriousness of the pandemic and the appropriateness of the pandemic response. Some Australian research suggests that pandemic influenza cases in hospitals and ICU had similar illness severity and death rates to those with seasonal influenza. While seasonal and pandemic influenza (who are mostly younger) patients might have the same outcome once they are admitted to hospital or ICU, what the hospital and ICU focused studies couldn’t measure was whether infection with pandemic influenza increased their chance of admission to hospital or ICU in the first place.
In research published in the same issue of the Medical Journal of Australia, we compared the risk of ICU admission among people in NSW infected with the usual seasonal influenza that was circulating at the same time as the pandemic strain was circulating. We found that people infected with the pandemic strain were five times more likely to be admitted to an ICU than those infected with routine seasonal strains.
Studies of antibodies against pandemic influenza in the community in Australia and overseas is suggesting that perhaps one third of people were infected with pandemic influenza with higher rates in children and lower rates in adults. These infection rates are much higher than the influenza illness rates we saw in the community and since most of the people with antibodies did not complain of an influenza-like illness it appears that most of the pandemic influenza infections had no symptoms.
So we have weathered the first wave of the pandemic with around 200 deaths, nowhere near the worst case scenarios of 44,000 deaths estimated based on the 1918 influenza pandemic.
While the 2009 pandemic influenza virus appears much milder than the 1918 strain, it is difficult to compare the two because of the advances in society and medicine over the last 90 years. While we have many people living longer with immune compromising diseases today, the immunity of the general population is higher due to good nutrition and better living conditions.
Many Australians will have been saved from a fatal post-flu bacterial pneumonia by a simple course of antibiotics prescribed by general practitioners, many will have been saved by expert mechanical ventilation in intensive care units and many of the patients who received ECMO, or heart lung bypass treatment, would almost certainly have succumbed to the virus without this treatment. There is emerging controversy over how effective the antiviral agent Tamiflu is in preventing fatal outcomes, but it likely also played a part in moderating this pandemic.
It is tempting to describe the initial pandemic responses as an over reaction, however, the initial reports from Mexico cited devastatingly high death rates and in public health emergencies it is important to surge the response and then wind it back as necessary. Fortunately, health authorities were able to recognise that this was a “mild in most, severe in some” pandemic and set aside the old pandemic game plan to focus on protecting those most at risk.
Given that there was probably widespread transmission of the pandemic virus in Australia before it was first detected it is still unclear what contribution public health interventions such as contact tracing, antiviral treatment, isolation and quarantine made to moderating the pandemic. If public health interventions did slow transmission of the pandemic virus, their greatest benefit may have been to smooth the pandemic peak and ease the number of cases admitted to hospitals and ICUs to help them cope. We can always learn from our pandemic response but it is clear that the pandemic virus was more likely to put young people in hospital and five times more likely to put a patient in ICU compared to seasonal influenza.
Now as we await the second wave to hit Australia in 2010 we are fortunate to have an effective pandemic vaccine. It can provide protection for both those with known risk factors for severe disease and for the perhaps 30% of us who have no known risk factors who may still be among the unlucky minority who will require the services of an ICU this winter if infected with pandemic influenza.”
• Dr Craig Dalton is a conjoint senior lecturer in the School of Medical Practice and Population Health at the University of Newcastle, and chief investigator on the national Flutracking.net influenza surveillance program. The opinions expressed are his own.
A wrap of other recent news in pandemic flu:
• Millions of doses of the Commonwealth’s swine flu vaccine could expire as people opt for the new seasonal flu vaccine, which provides broader protection for the year ahead, according to this report in The Age. Dr Peter Eizenberg, a GP and former member of the federal government’s immunisation committee, said a significant proportion of the government’s 21 million doses could go to waste now that the new seasonal flu vaccine had arrived.
• Meanwhile, CSL is doing very nicely, thank you.
• And this survey suggests that those most likely to have had the pandemic flu vaccination may have been those in least in need of it – given the evidence of prior immunity in elderly people. This study, released by the Australian Institute of Health and Welfare and funded by DOHA, found the uptake of the H1N1 vaccine was three times as high in those aged 65 years and over (42%) than in those aged 18–64 years (14%).
• A recent Canadian study whose authors concluded: “Our findings offer experimental proof to support selective influenza immunization of school aged children with inactivated influenza vaccine to interrupt influenza transmission. Particularly, if there are constraints in quantity and delivery of vaccine, it may be advantageous to selectively immunize children in order to reduce community transmission of influenza.” This is one public health blog’s take on the findings, as well as how it was reported in the New York Times.
• A British news report on recent Cochrane Collaboration review raising questions about effectiveness of influenza vaccination in elderly.
• Meanwhile, the latest WHO Update doesn’t suggest there is much evidence of the “second wave of infection” that we’ve been warned about in recent times. It says: “In the temperate zone of the southern hemisphere, overall influenza activity remained low, with sporadic detections of pandemic and seasonal influenza viruses”.
• And the latest European data, comparing activity between week 40/2009 and week 07/2010 with historical data where available, shows:
- In most countries that reported data, levels of influenza activity are well below recent pandemic peak levels and across most of the European Region, the first wave of pandemic influenza activity is considered to be at an end.
- In 19 of 22 countries reporting five or more years of data, the peak clinical consultation rates that were observed during the 2009/2010 pandemic season did not exceed peak clinical consultation rates observed during the previous years. However in several countries, clinical consultation rates did exceed recent historical peaks within some younger age groups.
- 4 572 laboratory-confirmed deaths associated with pandemic (H1N1) 2009 had been reported to WHO/Europe. Although these are underestimates of the actual number of deaths associated with pandemic H1N1 (2009) virus infections, these crude estimates of mortality suggest similar rates to those observed in countries during the winter season in the southern hemisphere.
• A Wall Street Journal report on the “flu season that fizzled”
• Meanwhile, the US plans to roll out mass seasonal vaccination
• And in Ireland, children have reportedly missed their vaccinations against measles, mumps and rubella because the programme fell behind as healthcare staff tried to cope with the demand for the swine flu jab.