In this part, I am going to talk about the value of hygiene and other personal interventions. The objectives of this session are: to identify the modes of pathogen transmission that can be prevented by hand hygiene and masks; to describe a basic case-control study; to discuss the role of hand hygiene and masks in control of respiratory viruses. Improvements in basic hygiene and sanitation have played a major role in the reduction in burden of infectious diseases in modern times. For pathogens spread through the fecal-oral route, like cholera and other diarrheal diseases, improved hygiene can effectively prevent transmission and control epidemics. For respiratory pathogens that are typically spread through contact and respiratory droplets, simple interventions can also be effective as we will see later in this part. An important early figure in the application of hand hygiene in medical settings was Ignaz Semmelweis, a physician in Vienna in the 1840s. In Semmelweis’ hospital, doctors conducted autopsies in the early morning, before attending the obstetric clinic. Semmelweis theorized that decaying matter, which he called cadaverous material contaminated the hands of doctors who had recently conducted autopsies on women who died from puerperal fever. This matter was then brought into contact with women who were about to deliver. Semmelweis noted that mortality rates in his hospital in Vienna were much higher than in Dublin, since the advent of pathological anatomy in 1823. He also noted that annual mortality rates from puerperal fever were higher in the first clinic, staffed by doctors, compared to the second clinic which was staffed by midwives after 1842. Semmelweis proposed and implemented an intensive hand washing intervention in 1847, and mortality rates immediately decreased. You would have thought that Semmelweis would have been feted for this important breakthrough, but by challenging accepted medical practice he made many enemies, perhaps not helped by his difficult personality. In a sad ending to this story, he was forced out of the hospital in Vienna, and died a few years later in a mental asylum. The hospital reintroduced early morning autopsies, and Semmelweis’ contribution was not fully recognized until some years after his death when hand hygiene gradually became accepted as a basic measure in infection control. Surgical face masks were first introduced in surgery more than 100 years ago, with the intention of protecting patients from any bacteria shed from respiratory droplets from the wearer's mouth and nose. This is known as source control, because the idea is to control the source of any potential infection. Nowadays, surgical masks are often used for another reason, as part of personal protective equipment, to protect healthcare workers from infection while treating patients with infectious diseases. Other components of personal protective equipment can include gowns, gloves, goggles, and face shields. In 2003, a new coronavirus emerged which caused a global epidemic of severe acute respiratory syndrome, abbreviated as SARS. One urgent question early in the SARS epidemic, was about which infection control measures were necessary to protect health care workers against infection. A number of studies were conducted, and I will discuss one such study conducted by Dr. Seto and colleagues in Hong Kong. The investigators conducted what is called a 'case-control study'. They identified 13 infected health care staff, with documented exposure to SARS patients, and interviewed them about the preventive measures they had taken while they had cared for the specific patients subsequently diagnosed with SARS, whether or not SARS had been diagnosed at that time. Two of the 13 staff reported wearing a face mask, 4 reported wearing gloves, none reported wearing a gown, and 10 reported hand washing. It is difficult to make any conclusion based on this information alone, what we need is a comparison group. So the investigators also interviewed 241 non-infected staff to get a better picture of the type of behaviours prevalent in the hospital staff at that time. This group is called a control group. In the control group, all behaviours were more commonly reported compared to the cases. We can quantify the differences in various ways, one of the most common is through odds ratios which here we can interpret as risk ratios. Significant differences between cases and controls were identified for the use of face masks and hand washing, and for all 4 measures combined. The authors concluded that these basic infection control measures, and particularly the use of face masks, could adequately protect health care workers against SARS. We can take a moment to think about the limitations of this study, and other similar studies. First, because the cases and controls were interviewed about their past behaviours, their responses might have been affected. For example, cases might have been less likely to report preventive measures since they know they were infected. Second, the behaviours are correlated with each other, and with other factors such as level of training and experience and it is difficult to determine which factors were most important in reducing the risk of infection. Nevertheless, this type of study can be done very cheaply and easily, and can provide timely information to guide infection control. In addition to their importance in the hospital setting, personal protective measures such as the use of face masks and hand hygiene can also be used in the general community. Widespread use of surgical face masks in the community is a seminal image during emerging respiratory disease epidemics and pandemics. For example, in SARS in Hong Kong in 2003, and in Mexico in 2009 at the start of the swine flu pandemic. However, the effectiveness of these measures in the community is less certain, with controlled trials generally identifying limited benefits of these measures. Recent reviews of hand hygiene and face masks against influenza found very modest benefits, consistent with recent studies suggesting that influenza viruses may sometimes spread through very fine respiratory droplets, which can remain suspended in the air for some time and can pass around or even through face masks. For emerging pathogens, the effectiveness of these measures would depend on the way in which they are spread and their transmissibility.
