Folklore had it that tuberculosis was spread by vampires and the first person to contract it within a household would slowly drain the life out of the remaining family members.
In the 1800s, TB was responsible for 1 in every 4 deaths in Europe. Currently, one third of the world’s population is infected with TB majority of which is in Asia and Southern Africa.
As of 2015, there were 1.5 million TB related deaths worldwide, a significant reduction in the death rate since the introduction of antibiotics used in the treatment of TB, 70 years ago, but still a leading killer of persons infected with HIV.
Data from 2014 have shown that HIV claimed the lives of 1.2 million people, a third of which had TB as co-infection. In the same year, TB surpassed HIV in causing deaths from infectious diseases, according to a World Health Organization (WHO) report.
WHO reports also says the prevalence of TB in Tanzania in 2014 was estimated at 270/100,000 indicating a decline compared to 295/100,000 in the first national tuberculosis prevalence survey the previous year.
Though there are no reports about the survey last year, the general trend shows a downfall in the number of TB victims in Tanzania, a country that still shares the heavy burden.
There has also been a shift in the disease epidemic to the older population, with the prevalence rate highest among those aged more than 45 years, a trend not prevalent in other African countries.
It is a tendency that owes the increased life expectancy where the elder adults whose TB infection may get reactivated are more vulnerable to infection than younger ones with higher immunity. Diabetes, which is more dominant among the old generation than the younger one also plays a vital role in lowering immunity.
TB infection is acquired via inhalation of aerosolized droplets from an infected person coughing, talking, sneezing or singing. The risk of infection is related to how infectious the patient is, duration of exposure, proximity to the infected person, how well ventilated the area is and the degree of crowding.
The risk of infection is also increased in persons with low immunity, such as HIV infected, elderly and children less than 5 years of age. However, in less than 10 per cent of people infected with TB develop its active form.
Other forms of TB are multi-drug resistant (MDR-TB) and extensively drug- resistant tuberculosis (XDR-TB). MDR-TB occurs when there is resistance to two of the most powerful drugs used in treatment.
This may develop when there is mismanagement of TB drugs or a direct infection from a person with MDR-TB. On the other hand, XDR-TB which is a form of multi-drug resistant TB with additional resistance to more anti-TB drugs (including second-line) is much more difficult to treat as it responds to even fewer available drugs. In 2014, 480,000 people worldwide were reported to have MDR-TB and 9.7 per cent of those were said to be XDR-TB.
Reported potential transmission of TB and other infections such as Severe Acute Respiratory Syndrome(SARS), which led to an outbreak in Asia with multiple deaths between 2002 and 2003,have greatly caused concern and anxiety among travelers and public health authorities.
Air travel has greatly increased over the last decades with millions of people flying annually. It is impossible to screen all passengers for TB before flights especially given the non-specificity of symptoms in some cases and the long incubation period of the disease.
Some embassies require screening for TB at the country of origin and upon arrival at the destination country. However, a potential traveler may be screened and found to be negative and develop TB between the time of screening and travel date. In countries that screen for TB upon arrival, persons may then only be diagnosed to have TB only after they have travelled.
So, should you be worried about TB if you are on a long flight and the person next to you has a cough? In the 1990s, there was major concern over transmission of TB from infectious travelers to other passengers during long flights.
The WHO published the first guidelines on TB and air-travel to address these concerns. According to the guidelines, there is evidence that transmission of TB may occur from an infected person during long flights but the risk is limited to persons in close proximity to an infected person and during long flights (8 or more hours).
Close contact would entail being seated on the same row as an infected person or two rows in front or behind them. Having stated that, no clinically or bacteriologically confirmed case has been identified as a result of air-travel related exposure during flight.
Ventilation is a key determinant in the risk of transmission and it is said that cabin air is cleaner than air in most buildings. Therefore risk of acquiring TB during air travel is similar to risk associated with other activities where contact with an infected person may occur such as at social gatherings in enclosed spaces.
Interestingly, smoking flights ventilation systems involve 100 per cent fresh air while non-smoking flights use 50 per cent re-circulated air. When the re-circulated air is passed through filters before being mixed with outside air and re-entering the cabin.
Well-functioning filters on modern aircrafts are able to remove any potential tuberculosis bacteria. There is also currently no evidence to show that re-circulated air increases the risk of transmission of infectious diseases on aircrafts.
Seeing as it is unrealistic to expect airline companies or embassies to screen all prospective travelers for tuberculosis, all persons with infectious TB should be advised not to travel via aircraft.
If air travel is absolutely necessary then they must opt for non-commercial flights. Alternative private transport should also be considered such as private ambulance when possible.
It is also unrealistic to deny travel to persons undergoing treatment for TB as they become non-infectious after two weeks of treatment in drug-susceptible cases. Sadly, TB notification to airlines is low at about 0.05 per 100,000 long-haul passengers over a five year period according to WHO.
If during a flight a person is suspected to have TB then they must be reallocated to a seat without close contact with other passengers. They should also be advised to cover nose and mouth either with a surgical mask and if not possible with disposable tissues.
The pilot is also required to inform the International Health Regulation (IHR) authorities that they are carrying such a case so that adequate measures may be undertaken on the ground.
***Dr Sanaa S. Said is a physician based in Zanzibar. She is a specialist in Internal Medicine, Tropical Medicine and Hygiene. Contacts: [email protected] tel. 0772466047