Last week, the Department of Education preemptively suspended classes in Metro Manila public schools due to increasing cases of influenza-like illnesses among children. This was done in an attempt to interrupt transmission and to disinfect classrooms and other school facilities. Many private schools followed suit. In the meantime, the Department of Health clarified that the increase in cases was not unusual for this time of year, and so it was not technically a flu outbreak. It reiterated measures to decrease the risk of infection, such as staying home if you are sick and wearing a mask, especially if you have chronic health problems.

What is an influenza-like illness (ILI)? The World Health Organization defines ILI as any illness that causes a fever of 38C or higher plus a cough. This is a very nonspecific definition and can include non-infectious causes of fever and cough. From a practical medical standpoint, doctors usually refer to ILIs as a syndrome that is caused by respiratory viruses or bacteria that cause fever as well as cough, colds, and other respiratory symptoms.

Historically, influenza has been the most likely cause of ILI and has also been the easiest to diagnose due to the availability of influenza rapid tests. If a patient had an ILI but tested negative for influenza, he or she was presumed to have one of the other causes of ILI. During the Covid-19 pandemic, influenza was displaced by SARS-CoV-2 as the most common cause of ILI. The use of RT-PCR technology during the pandemic also gave rise to syndromic respiratory panels, which could detect different viruses and bacteria that cause ILI. These include two serotypes of respiratory syncytial virus (RSV), and several kinds of paramyxovirus, human metapneumovirus (HMPV), adenovirus, rhinovirus, as well as the bacteria that cause pertussis and atypical pneumonia. Including these infections under ILI facilitates surveillance of respiratory illnesses by the Department of Health, and they can keep track of any unusual rise in cases. However, the ILI definition can miss some viruses, such as RSV, that don’t always cause fever, especially in mild cases. When this happens, an outbreak can still be detected if there is an unusual clustering of cases and if they get picked up by clinical laboratories doing testing.

It is important to differentiate ILI from the common cold because ILIs have a greater propensity to progress to severe disease. Common cold viruses overlap with ILI viruses depending on the virulence of the virus and the immune status of the host. For instance, in a healthy host, HMPV just causes a self-limited cough and cold for a few days, and it goes away without any treatment. In an immunocompromised host, it can cause fever and pneumonia, which can be life-threatening.

Influenza itself is quite debilitating even in healthy hosts, and it takes a few days to recover and return to school or work. Influenza causes high fever, chills, body aches and pains, as well as cough and cold. The risk of severe complications such as pneumonia, especially in unvaccinated elderly persons, is what makes influenza a considerable health threat. Even though the flu does not have a very high mortality overall (between 0.13 to 1.36 percent), the absolute number of deaths can average nearly 650,000 per year because millions of people are infected annually. Fortunately, we have yearly vaccination for influenza, which is effective for decreasing severe disease. The vaccines don’t work very well in preventing infection, but they significantly decrease the risk of hospitalization and severe infection. Since we live near the equator, both northern and southern hemisphere vaccines become available to us every six months, but you just have to choose one, and it should be good for an entire year.

Aside from influenza, Covid-19 is still very much around and usually presents as an ILI, especially among the elderly and those with comorbid conditions such as diabetes, heart disease, and chronic lung problems. There are still no updated Covid-19 vaccines locally, but the original vaccine and boosters continue to substantially decrease the risk of severe disease compared to those who never got any vaccination. Medications such as nirmatrelvir-ritonavir (Paxlovid) and remdesivir continue to work on the latest variants, but these medications are expensive. Vulnerable populations should consider wearing masks in crowded areas, especially during flu season, when it is very difficult to distinguish which respiratory virus is circulating. In fact, I often see patients with mixed infections. I recently had a patient in the hospital with flu and RSV infection. Fortunately, he was vaccinated for the flu, and he did well and was discharged after a few days.

RSV isn’t new and has been detected in the Philippines for decades, but is being diagnosed more frequently nowadays because of syndromic respiratory panels. As I wrote in a previous column, it can cause very bad pneumonia among elderly people, especially those with chronic lung or heart disease. Fortunately, there are two RSV vaccines (you only need one shot from either) available, which are highly efficacious at preventing hospitalization among those 50 years old and above.

HMPV and the other respiratory viruses are a bit tougher to diagnose, although some of them are on the respiratory panels. Unfortunately, there are no effective medications or vaccines for these, although some are in the pipeline. Your best bet at avoiding these illnesses is by wearing a mask, washing your hands, and avoiding excessive stress on your immune system.

What about the school breaks that were done to interrupt transmission? Do these really work, as opposed to just having schoolchildren wear masks? The evidence is mixed, and we know that online school is never as good as real face-to-face school. By the time a decision is made to shut down classes due to many cases of ILI, most children would have already been exposed. The only benefit may be that they can rest at home and recover faster. It would not be practical to shut down earlier when it could actually interrupt transmission, since too many days would be lost and there would be too many false alarms. My expert opinion is that, outside of a new pandemic situation, we should just let our kids go to school even when respiratory viruses are circulating and equip them with the tools to keep themselves healthy—masks, good hygiene, good cough and cold etiquette. Make sure they are fully vaccinated and well-nourished, and the occasional sniffles will be taken care of by a healthy immune system, even as the children learn their lessons in front of their teachers. After all, we don’t need them to just have healthy bodies… We also need them to have healthy minds.