Outbreaks of hepatitis C, like the recent one at the Singapore General Hospital (SGH), are different from outbreaks portrayed in Hollywood blockbusters like Outbreak or the more recent Ebola epidemic in West Africa, or, closer to home, the severe acute respiratory syndrome or Sars in 2003.
These outbreaks were all characterised by an explosion in the number of cases, high mortality and heartbreaking images of patients on respirators. Hepatitis C outbreaks are different.
To begin with, hepatitis C and Sars are transmitted differently. While one can become infected with hepatitis C only if the virus gets into one's bloodstream, say, through contaminated needles, one can get Sars simply from someone coughing in your face or caring for someone with the illness.
To complicate matters, hepatitis C infections can often go unnoticed. It is a silent infection, with only one in five patients developing acute symptoms such as fatigue, vomiting or jaundice after a period of two weeks to six months. By contrast, Sars sufferers exhibit terrible symptoms, such as shortness of breath and fever within a few days of infection.
When there are no symptoms, hepatitis C infections can be detected only by blood tests: both antibodies and viral particles can be measured. It is, therefore, possible for a hepatitis C outbreak to go undetected for a long period. And this is why for high-risk groups (for example, haemodialysis patients) there is ongoing surveillance to check for hepatitis C infections.
Indeed, hepatitis C epidemics have been called "shadow epidemics" by epidemiologists (experts who study the patterns, causes and effects of health and disease conditions in defined populations).
About 15 per cent to 25 per cent of those infected with hepatitis C are able to rid themselves of the virus through their own bodies' immunity actions; the rest remain infected for life unless treated. And among those who do not receive treatment, up to a third develop cirrhosis (hardening) or cancer of the liver decades after they became infected.
Confronted with a silent infection like this, most countries have in place programmes to prevent the spread of hepatitis C. In Singapore, as in many countries throughout the world, routine testing is done by the blood bank to be sure its blood is safe for transfusion to others.
Blood that tests positive for hepatitis C is rejected and the donor referred for further investigations and treatment.
In addition, renal patients on haemodialysis are routinely screened for hepatitis C. Current best practice is to screen new renal patients for hepatitis C antibodies, with the screening repeated once every six months thereafter. Patients who have converted from a negative screening result to a positive one are considered new cases of hepatitis C infections.
In the United States, the Centres for Disease Control and Prevention (CDC) has reported 22 hepatitis C outbreaks in healthcare facilities for the period 2008 to last year. There were a total of 239 cases. The largest outbreak saw 46 cases; the smallest, two. Half of the 22 outbreaks occurred in a renal disease setting - a total of 79 cases after testing 1,833 renal patients.
Underlining the challenge of hepatitis C infections being "silent", one of these outbreaks in a haemodialysis facility in Maryland was identified only after an audit was carried out in 2009. Subsequently, a total of eight cases occurring from 2007 to 2009 were uncovered. All eight cases did not exhibit symptoms. The source of the outbreak was not conclusively identified but observations of work practices indicated the need for greater vigilance in infection control practices.
Another global review of outbreaks in dialysis units uncovered 45 outbreaks in several countries - including France, Germany, Spain, Italy, Hungary, Japan and Thailand - from 1994 to this year. There were a total of 335 cases, with the largest outbreak being in Thailand where out of 184 initially uninfected renal patients, 51 became infected over a three-year period.
Confirming an outbreak in itself takes time because patients may take up to six months to develop symptoms, and genetic analysis of the virus is required to confirm that patients in a cluster are related. Hence, in some outbreaks in the US, it took weeks if not months for reports of the outbreaks to surface.
No single cause was discovered in most of the outbreaks. Investigators either could not pinpoint the exact cause or causes, or identified multiple lapses. These included cross-contamination between clean and dirty areas, failure of hospital staff to consistently change gloves and perform hand hygiene, and breaches in environmental cleaning and disinfection.
In the US, the CDC also reported some large outbreaks in healthcare settings other than renal wards.
One of these was in a hospital in New Hampshire which involved 32 patients and one healthcare worker. After more than a year of extensive investigations, the source of the infection was traced to an infected healthcare worker who stole narcotic pain medication intended for patients for self use.
Another major difference between Sars and hepatitis C is the risk they pose to the public. Sars can spread like wildfire. Hence, although the 2003 outbreak in Singapore was mostly limited to a spread within hospitals, the public health authorities, in Singapore and around the world, sought to contain further community spread by advising the public to keep out of crowded places and to practise good personal habits like hand-washing and wearing a mask.
The spread of hepatitis C requires infected blood and a break in the skin, as may happen when sharp instruments with infected blood are used. The risk to the public is therefore small. The priority in outbreaks of hepatitis C is to focus on tightening processes within hospitals, and less on containing community spread. Unlike in the case of even flu epidemics, the health authorities around the world do not conduct major public education campaigns to promote personal hygiene and socially responsible behaviour in response to outbreaks of hepatitis C.
Investigations into the SGH outbreak are ongoing and it would not be appropriate for us to comment on the specifics of the matter. Though in many outbreaks in other countries the authorities have been unable to specify the causes, or do it with certainty, we hope the Independent Review Committee that was formed to investigate the SGH outbreak will be able to narrow down, if not pinpoint, the actual source of infection. This will go a long way towards helping us identify useful lessons to strengthen the healthcare system.
•Professor Chia Kee Seng is Dean of the Saw Swee Hock School of Public Health at the National University of Singapore and Professor David Heymann is chairman of Public Health England, an executive healthcare agency in Britain.
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