Characteristics of tuberculosis in older patients

INTRODUCTION

Tuberculosis (TB) remains a leading threat worldwide, with an estimated global total of 10.6 million cases reported in 2020 resulting in approximately 1.3 million deaths the same year. Low- and middle-income countries carry about 95% of the global TB disease burden.^[1,2] TB incidence rate is estimated to have increased by 3.6% between 2020 and 2021 worldwide.^[2] In 2019, more than 29,000 cases of TB were reported in Cameroon.^[1,3] The TB incidence rate in Cameroon usually peaked among the younger population, especially in people living with human immunodeficiency virus (HIV) whose incidence rate varies between 31 and 69 cases/100,000 people.^[3-5] Despite increased awareness in vulnerable groups such as people living with HIV and the widespread use of antiretroviral therapy (ART), TB in older adults is emerging as a global health issue, and TB control in this group is a major challenge for TB programs.

TB notification rates are higher among those aged 65 and above with those over 80 years having the highest incidence.^[6] It is argued that older people may have increased susceptibility to active TB and to the reactivation of latent TB infection.^[7] This increased susceptibility is being driven by changes in immune functions, malnutrition, and comorbidities such as diabetes mellitus but also socioeconomic vulnerability and reduced access to health services.^[8] Many studies have demonstrated that TB in the older is likely to follow a non-classical course.^[9] Pulmonary TB (PTB) in the older has a low positive rate of sputum smear making diagnosis difficult and more likely to have delayed diagnosis.^[8-11] Nearly, 40% of TB cases among people over 65 years experienced a diagnosis delay of more than 4 months.^[12] Furthermore, they are more prone to treatment-related adverse effects leading to treatment default, higher rates of retreatment, drug resistance, and mortality.^[8,13]

The older population is expected to double in the majority of African countries during the current decade.^[14,15] The ongoing epidemiological transition and increasing life expectancy are bringing about new challenges for the success of TB programs as these older patients are reservoirs for the continuous spread of the disease. A better understanding of the pattern of TB in older adults in Cameroon can provide substantial information on the course of TB and also improve care for elders in our setting where patients are managed with important financial restraints. Thus, we aimed to determine how TB characteristics differ between older and non-older people in the North and West regions of Cameroon.

MATERIALS AND METHODS

RESULTS

DISCUSSION

The present study has highlighted the characteristics of TB in older adults in Cameroon. In contrast to previous studies on older TB patients conducted in Cameroon, this study included a large cohort of TB patients from two regions of the country and is more likely to be representative. In our cohort, older patients with TB accounted for a low proportion of all TB patients. However, they were more likely to have SNPTB and EPTB. They had lower rates of lymph node TB and HIV coinfection compared to the non-older. The majority of older patients were under the “new case” treatment regimen.

The proportion of older people with TB in our study was lower than the 12.8% and 12.7% reported in Senegal and Nigeria, respectively.^[10,17] It is also far from the 16.6% reported in India.^[11] The proportion of TB cases in older adults varies widely across various settings. Although the reasons for these discrepancies are not clear, diagnosis of TB is a challenge in the older population. Indeed, TB in the older can easily be paucisymptomatic or atypical due to age-related immune changes and comorbidities, thus making diagnosis difficult. Low reports of TB in older people in our setting are probably hindered by a low suspicion index as other conditions like cancer are usually called to mind in the presence of clinical features like weight loss that can also be described in patients with TB. Furthermore, the cut-off used to define the older population, in other studies conducted in Africa is 60 years and over while we used the cutoff of 65 years and above in our study.

Our study has shown that older people were more likely to present with SNPTB. This is consistent with other findings in Mexico, Nigeria, Tanzania, and India.^[8,10,11,18] This high rate of SNPTB can be explained by age-related changes in lung functions especially decreased mucous production. This can impede their capacity to produce adequate sputum. Sputum analysis is a cornerstone in the early diagnosis of patients with suspected TB but access to TB diagnosis by sputum is a major issue in Cameroon even in non-older patients.^[19] Indeed, despite the implementation of molecular testing, about 10–25% of suspected PTB in Cameroon are treated as SNPTB.^[19,20] Furthermore, the lack of routine culture confirmation in our country does not allow the detection of acid-fast bacilli in sputum.^[21] This higher sputum smear negativity at baseline reported in older patients is a matter of concern as it may delay the diagnosis of TB. Flexible bronchoscopy has significantly improved the diagnosis of TB in older patients who cannot provide adequate sputum.^[22] However, its use remains limited in our setting, due to geographical and financial constraints.

We reported a higher rate of EPTB among the older group in comparison to the non-olders. Our prevalence was less than the 20% reported among patients aged ≥51 years with bacteriologically proven EPTB in the Littoral region of Cameroon.^[23] However, our findings are in line with those of Nagu et al. in Tanzania and Niu et al. in China who reported 10.5%^[18] and 11.5%^[24] of EPTB cases among older patients, respectively. It is not clear if older patients may have increased susceptibility to the hematogenous dissemination of Mycobacterium tuberculosis. However, EPTB is characterized by various clinical presentations depending on the involvement. It is possible that extrapulmonary localizations such as lymph nodes or pleural involvement were more suggestive of TB in our study thus maybe the index of suspicion was higher in the older group.

Older patients had lower rates of HIV-co-infection than the non-older group. This is consistent with other studies conducted in Nigeria and Senegal.^[10,17] However, our findings should be interpreted by taking into account the low perceived risk by clinicians and older people themselves.^[25,26] Indeed, HIV is usually perceived as a condition of the non-older but there has been increasing interest in understanding the course of HIV in aging in various settings. Low levels of HIV testing in older people contrast with the changing epidemic in Cameroon. The older population is growing in HIV care units in Cameroon, reaching 15% in some regions.^[27-29] HIV is a known risk factor for TB disease as well as TB associated-mortality^[3,5,30] despite increasing ART coverage in the country. Further research is needed to determine the profile and burden of TB-HIV coinfection among older patients.

Our study has many implications for the national TB program. Although diagnosis in older is a challenge, it is probable that TB cases among older patients are underreported due to a low index of suspicion among clinicians. These older patients are reservoirs for the continuous spread of the disease despite increased awareness in other vulnerable groups. Another important concern is the lack of recording comorbidities especially in the older group. This might be an opportunity to call for close collaboration with another program like the one in charge of the non-communicable diseases of the Ministry of Public Health, to improve recording in the existing registry. This will also be relevant to assess the impact of nonHIV comorbidities on the course of TB among older patients.

CONCLUSION

Older patients with TB in the North and West regions of Cameroon are likely to present with SNPTB and EPTB. They are less likely to have TB-HIV coinfection in comparison to non-older patients. Strategies to maintain a high index of suspicion among clinicians and the community are not only relevant but also necessary to enhance the recording of TB cases among older patients, thus reducing diagnosis delays.