The burden of disease

16 March 2016

Here in Hong Kong, with our dense population and constant jumble of people on the streets, the threat of infectious disease looms large. Going back even to colonial days, infections and epidemics have been a part of Hong Kong’s history. The causative pathogen of bubonic plague, Yersinia pestis, was first described here, influenza outbreaks throughout the 20th century came through and out of Hong Kong, and the panic caused by SARS still shows itself on the ‘sanitised every hour’ stickers found across elevator buttons and door handles across the city. 

Benjamin Cowling (Croucher Senior Research Fellowship 2015) studies the epidemiology of respiratory infections, with a particular focus on influenza. One area of Prof Cowling’s research is on the burden of disease; that is, how many people get infected, how many get sick, how many are hospitalized, and how many die. Quantifying the impact of influenza on a population reveals information not just about the spreading and infection patterns of the virus itself, but also the effects that an epidemic or even just the regular, annual flu season can have on the economy and the potential strain put on hospitals. One tricky part of studying influenza is that the deaths caused by the flu are often in elderly patients who may be simultaneously suffering from other diseases, giving the flu the chance to strike at a weakened immune system, or die from something else entirely, like pneumonia or cardiovascular diseases, triggered by the flu infection.

Prof Cowling also traces and studies the ways in which infection spreads. While it’s known that a sneeze or a cough can pass on the flu through fluids sprayed into the air, there is debate about the potency of small particles to pass on the disease. Tiny, mist-like particles, considered by some to be too small to transmit the virus, may be considered harmless by many as they can easily be blown away by air currents but Cowling’s research has shown that about half of influenza transmission in households may be caused by these small particles. This has many implications for flu prevention. Surgical masks, a common sight in this city for the prevention of disease transmission, may have a very limited effect against influenza if these small particles are able to go around the edges of the masks or even slip through the pores in the mask material.

The Case for Vaccinations

It is also important to track the contact patterns that lead to the spreading of disease. As it’s known that children generally have much higher contact rates, due to constant contact with each other in school, the Hong Kong government has been considering a territory-wide scheme to vaccinate all schoolchildren. While kids don’t suffer the most from the disease, that is, the vast majority of school age children have mild infections without any complications, they are one of the biggest transmitters of the disease and so vaccinating children could have a huge impact on controlling the spread of disease. Research in the UK has suggested that vaccinating children could actually deliver considerable economic advantages. Fewer kids have to go to the doctor, parents don’t need to miss work to stay home and take care of their kids, and on top of that, increased vaccination means reduced spread of the disease to people of other ages.

In addition to the question of whether or not to vaccinate children, Prof Cowling is also doing research into the benefits of vaccinating the elderly twice each year. Hong Kong has two flu seasons, one from roughly January to March and the other from July to August. The severity of these flu seasons can be predicted based off of identifying the strain of the flu from early infections and using known infection patterns to forecast how many people are likely to get sick. Now, the elderly are vaccinated before the winter flu season. The question is whether or not there is a considerable benefit gained from vaccinating the elderly before the summer flu season. Vaccines always carry a tiny risk of unpleasant side effects, and so it must be assessed whether the vaccination for the summer season provides additional benefits that justify the cost and the risk of that second vaccination.

Hong Kong’s unique situation makes it a special place to study infectious disease. The dense population and frequent contact between people make it more difficult to translate studies done in other countries back to Hong Kong. Prof Cowling’s own research has resulted in some somewhat unexpected results. Several years ago Prof Cowling conducted a vaccine trial on school age children. Some were given a flu vaccine and some were given a saltwater placebo. Over the course of a year these children were monitored, and at the end of the trial it was shown that the risk of flu in vaccinated children was up to 60% lower than those who were given the placebo. However, the overall rates of sickness were the same. The vaccinated kids had fewer instances of the flu but more instances of other common respiratory illnesses, like coughs and colds caused by rhinoviruses or coronaviruses. The kids given placebo, on the other hand, had higher rates of influenza infection but lower rates of infection from the other common cold viruses. Prof Cowling suspects that the stimulation of the immune system is responsible for this. After an infection, the immune system remains active and stimulated for a few weeks, providing a bit of extra protection while the body recovers. The kids given placebo may have come down with the flu, but this served to stimulate their immune system, providing protection from other common respiratory illnesses that may have tried to infect them later. These findings suggest that, if getting sick is inevitable (if it’s not the flu, it’s the cold and vice versa) then the UK findings that support vaccinating children from an economic standpoint may have less benefit here in Hong Kong where the higher population density and environment are conducive to more frequent common cold infections. However, vaccinations also curb the spread of disease. Even if there isn’t a direct effect on reducing illnesses in children, additional vaccinations could serve to slow down influenza’s spread in the community as a whole.

Anti-Microbial Resistance

Outside of his influenza research, Prof Cowling is also studying anti-microbial resistant pathogens, more threateningly called ‘superbugs’. These ‘superbugs’ present an almost doomsday scenario for the world; the more we use antibiotics to treat infection, the more likely it becomes that pathogens will evolve an immunity to the drugs. The WHO has cited global warming and anti-microbial resistance as the two biggest threats to the planet. If scientists’ fears about the growth of superbugs were to come true, medicine would be set back 100 years. The kinds of infections and diseases (dysentery, cholera, tuberculosis, typhoid, etc.) that used to cause the majority of deaths but now are easily treated with antibiotics would make a comeback, with immunity to our only defenses against them. Because of pharmaceutical companies’ unwillingness to invest in the development of new antibiotics, Prof Cowling is looking into other strategies to curb superbug growth. Tracking antibiotic usage, both on the patient level of making sure patients take their fully prescribed courses for example and on the physician level of monitoring when antibiotics are used and which ones are chosen. Antibiotic use in the animal sector also contributes to antimicrobial resistance, and can be more challenging to address.

One thing we have to do is convince politicians and policy makers to take action now.

Looking ahead, Prof Cowling cites the importance of appealing to politicians and policy makers. The threat posed by superbugs is one of the future. Action needs to be taken now, and it can be difficult sell something like the idea of raising taxes now so doctors can use other antibiotics, protecting us from a potentially devastating problem twenty or thirty years from now. Further complicating the difficulties in securing necessary policy changes is the visibility of the problem. Other diseases like Zika virus or HIV are much more in the public eye. The complications caused by antimicrobial resistance are usually borne by people already in a hospital, with an infection adding time to their stay or making their recovery more difficult. These problems are more insidious, acting more like a slow drain than a sudden outbreak, and because of this people are less likely to take notice and be scared into action. However, with the right kind of research that highlights both the economic and life saving necessity of new and different antibiotic protocols, change can be made.

Prof Benjamin Cowling joined the School of Public Health at HKU in 2004. Prior to moving to Hong Kong, he graduated with a PhD in medical statistics at the University of Warwick (UK) in 2003, and spent a year as a postdoc at Imperial College London (UK). Prof Cowling has been the Head of the Division of Epidemiology and Biostatistics since 2013. His research aims to integrate information on transmission dynamics at the individual level with disease burden, severity and dynamics at the population level. His latest research has focused on the modes of respiratory virus transmission, and the potential causes and implications of interference between respiratory viruses.

To view Prof Cowling's personal Croucher profile, please click here.