Better house ventilation and outdoor activity helps protect against Tuberculosis

CONCLUSION AND RECOMMENDATIONS

The seasonal variability of tuberculosis is quit clearly demonstrated by the epidemiological data;showing mostly a peak in notification numbers in early spring and summer months. This finding may have important implications, it seems that the risk of M. tuberculosis transmission appears to be the greatest during the winter months, particularly in overcrowded and poorly ventilated settings. There are several possible reasons of the seasonality of tuberculosis: serum vitamin D level variability, indoor activities, seasonal changes in immune function and patient or health care system delays in the diagnosis and treatment of tuberculosis. Additionally, seasonal variation in food pattern, age and sex are important factors which can play a role in tuberculosis notification variability. Further prospective studies are required to better understand the fundamental patho physiologic mechanisms underlying seasonal immune system competence and tuberculosis.

The knowledge of the role of environmental factors (infection, cold, etc.) or other triggers (indoor activity, vitamin D intake) could be used to improve prevention measures and educational strategies,especially in people with a risk of infection. People should be informed of the increased risk of disease transmission during the cold seasons, and educated about the importance of seeking health care if they develop tuberculosis symptoms. People should be informed about the importance of proper housing ventilation and the potential benefits of increased outdoor activity in natural UV light. Furthermore, people should be motivated to maintain health dietary habits including a nutrient rich in vitamin D. There is also a need to improve health accessibility of health care services, especially in rural areas in some countries. Clinical practitioners have to be educated on the importance of continuous and good surveillance and timely reporting of tuberculosis patients.

There are many gaps in the current knowledge, but it can be assumed that research on behavioral and physiological mechanisms and their effect on the seasonality of immune function are likely to provide important insight into the role of the environment in influencing health and well-being.

Food habits and seasonal rhythm of nutrient intake

It is well known that malnutrition increases risk of contracting tuberculosis and profoundly affects immune system functions.[1] This influence may vary according to the seasonal cycle, because the availability of food or in the amount of food intake during the seasons. One study conducted in the USA shows seasonal variations in the nutrient intakes and the meal patterns of humans. A marked seasonal rhythm with increased total caloric intake was observed, especially of carbohydrate, in the fall, associated with an increase of meal size and a greater rate of eating, but not found changes in winter and spring.[38] Another study conducted in Gambia found energy intake among women in the wet season was clearly inadequate, while in the dry season intake almost met energy requirements.[39] This finding may be linked with seasonal variability of tuberculosis particularly in wet season in Cameroon with high number of tuberculosis case notifications.

Additionally, vegetarianism and tuberculosis have been linked with increased incidence of tuberculosis among immigrants from the Indian subcontinent who live in the UK.[32] Vegetarian diets have been reported to be associated with deficiencies of certain minerals and vitamin in particular vitamin D. This kind of food (vegetarian) is common among Hindus due to religious restrictions.[41] That could be a contributing factor and may help to explain the seasonal peaking notification of tuberculosis among Indian origin patients in the UK. Recently, immigrated persons had a higher risk of developing tuberculosis disease than those who had been in the UK more than 5 years or who were born in the UK.[9,41] Thus, people may have latent tuberculosis which is reactivated when their vitamin D level is diminished due to the largely dark climate of the UK in addition to the absence of vitamin D diet resource as a consequence of vegetarianism.[4,21]

Share of the seasonality with other infectious diseases

Winter is known to be a season of respiratory infectious diseases, both viral and bacterial.[6] In addition, some infectious diseases exhibit frequent and shared patterns in the same season such as increased incidences of pneumococcal and meningitis during influenza season and the occurrence of streptococcal disease, varicella zoster virus infection, and bacterial super-infection in children with seasonal measles virus.[43] This frequency may contribute to explain a result of predisposition to infection with other pathogens in winter, which could be also a reason to the high rate of tuberculosis notification in Spain in late winter (February) and spring associated with flu viral infections as the authors suggest. That could also relate to increased admission of patients with respiratory tract infections in the UK and Russia during the winter season thereby, leading to the diagnosis of tuberculosis particularly in children. This diagnosis can be made by vigorously investigating children with existing respiratory complaints for possible tuberculosis.[6] The Influenza virus or other pathogens cannot cause tuberculosis, but may accelerate disease manifestation in patients with latent tuberculosis or increase susceptibility of individuals to infection and therefore, develop the disease faster than those without these diseases. The process is probably aggravated by an increasing frequency of coughing consequential from other winter viral and bacterial respiratory infections.[6] However, the general finding of this review coincides with this hypothesis due to the higher number of tuberculosis notifications in spring and summer especially among children.

Seasonal immunity competence

The exact mechanism of M. tuberculosis reactivation in a particular time of the year is still not well understood in most cases.[32] Recent evidence suggests that the immune system competencies vary through the year with significant periodicity in immune cell function and in the number of some peripheral blood leukocytes subsets.[5] In this regard, it is not surprising to see seasonal variability in tuberculosis manifestation with a peak of notification rates in spring and summer. Experimental studies findings support these observations. For example, the natural killer cells and CD4 T-cells have been reported to be increased in winter associated with an increased level of Interleukin-6.[5,33] This could be a reason for a better immune response against Mycobacteria in winter compared to summer, obviously not preventing infection, but allowing to control it in winter, whereas the infection later progresses to disease. Moreover, these findings consist with a study conducted in India, showing that the morbidity of tuberculosis is high in summer compared to winter.[34] In contrast, in Western Africa, CD4 cells count were low in children in the rainy season (winter).[35] That may give an explanation for a peak of tuberculosis notification in Cameroon during the winter season.

In addition, there is some evidence that the fluctuation in weather temperature during winter seasons may act on the respiratory epithelium by slowing mucociliary clearance and inhibiting phagocytosis, which then lead to increase the susceptibility to infection.[36] This may give us an explanation about the findings of this review regarding the peak of seasonal notification of tuberculosis cases and the possibility of infection during winter season.

Indoor activity

Generally man spends more time indoors in cold (winter) than in warm season (summer), which coincides with the scientific fact that overcrowding, increased humidity, and low airflow provide a suitable environment for M. tuberculosis to survive. Additionally, transmission is more likely during winter months due to diminished amounts of natural ultraviolet light. In summer season, the absorption of natural ultraviolet light is higher and can kill M. tuberculosis within a short time, while it can survive in darker conditions for a longer period. These properties of M. tuberculosis support the suggestion that most disease transmissions occur indoor. The fact that there are higher transmissions rates in winter followed by the development of disease several months later would be supported of the findings of this study.

Vitamin D status variability

The potential factor that has been suggested in most articles is the link between vitamin D level and impaired host immunological defence with the reactivation of latent M. tuberculosis infection.[4] Several studies from various regions, ethnic groups, and cultures show positive association between the serum level of vitamin D and susceptibility to TB infection or reactivation.[17] Serum vitamin D concentrations are significantly lower in TB patients compared with those in control groups. Several mechanisms have been proposed to explain this relation, most of them concerned with the possibility of the role of active metabolite vitamin D (25-(OH) D) in the hosts defence against human tuberculosis, thus suggesting that metabolite (25-(OH) D) can act to suppress the growth of M. tuberculosis through the induction of nitric oxide (NO) production by macrophages.[18]

Significant seasonal vitamin D level variations were observed in several communities, which reveal a variation of values for 25-(OH) D, increased during summer and spring, while gradually decreasing in autumn and winter.[19,20] Various authors are in favor of the idea that highest TB rates in spring and summer are associated with the seasonal variation of vitamin D level.[1,2,8] The significant observations of the seasonal peak of tuberculosis in Indian immigrants in Kuwait in late April was consistent with the findings of tuberculosis peaking from April to June in northern India. Also, it may well be that the immigrants from India have a very high proportion of TB and arrives Kuwait mainly in winter month while migrants from Sri Lanka and other low burden countries have a low proportion of TB and arrive mainly in summer.[2]

Several studies on vitamin D level variations suggest that heavy clothing in winter is considered as a barrier that can reduce ultraviolet radiation reaching the body and thus, the conversion of vitamin D. In addition, some cultural factors such as style of clothing (veiled clothing) were shown as potential factors which influence serum vitamin D concentrations, particularly in women. Women in some conservative cultures also tend to spend longer periods of time indoors.[21,22] According to these findings, one could hypothesize that women in some communities are more susceptible to TB than men as a consequence of vitamin D deficiency and/or duration of time spent indoors. Other studies conducted in various countries show that the vitamin D deficiency is more predominant among women regardless of age, lifestyle, and clothing (veiled).[23–26] This finding is contradicted by studies which show no significant difference between genders in seasonal notification of tuberculosis.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3068579/