Introduction
Since December 2019, a novel coronavirus SARS-CoV-2 has swept all across the world. Globally, it has infected 500 million individuals, leading to more than 6 million deaths [
1]. In the Philippines, more than 4 million people have been infected, with 64 thousand individuals expiring from the disease [
2]. The COVID-19 pandemic continues to strain the healthcare system in terms of cost, resources, and workforce. Because of its impact on public health, there is an ongoing need to elucidate the pathophysiology of COVID-19 and the risk factors that may impact its transmission, virulence, and associated clinical outcomes. COVID-19 commonly presents with fever, cough, dyspnea, fatigue, headache [
3], and disturbances of olfactory and gustatory function [
4]. Rarely, it may also present with vasculitis-like skin lesions [
5].
Early studies among patients with COVID-19 have identified hypertension as the most common comorbidity, suggesting that it may be an independent risk factor for increased severity and mortality among patients with COVID-19 [
6,
7]. According to the latest National Nutrition Survey done by the Food and Nutrition Research Institute (FNRI) in 2018, among Filipinos 20–59 years of age, the prevalence of hypertension was 19.2%. Among adults aged 60 years and above, it was pegged at 35% [
8]. These hypertensive individuals, constituting a sizeable bulk of the Filipino population, may be at higher risk for COVID-19 infection and disease progression.
Despite this, many earlier studies did not account for the confounding effect of comorbidities, such as diabetes mellitus, obesity, and coronary artery disease, that often cluster around hypertension. Succeeding studies since have shown heterogeneous results. Some studies showed that hypertension was an independent predictor of severity and mortality [
9,
10]. Others discovered that it was only a predictor when combined with another comorbidity [
11], while some investigators surmised that it was not a predictor at all [
12‐
14]. There is still a continuing controversy on the effect of hypertension on the COVID-19 disease process. To help address this knowledge gap and contribute to the growing fund of knowledge on COVID-19, we performed an analysis of data from the Philippine COVID-19 outcomes: a retrospective study of neurological manifestations and associated symptoms (Philippine CORONA Study) [
15] to elucidate the association between hypertension and clinical outcomes among Filipino patients hospitalized for COVID-19.
Discussion
The Philippine CORONA Study data paved the way for sub-studies that elucidated the impact of comorbidities on the outcomes of COVID-19, including studies on body mass index [
17], diabetes mellitus [
18], malignancy [
19], and stroke [
20]. Our findings from the Philippine CORONA Study data were consistent with the findings of past observational studies [
6,
7,
9,
10] showing that hypertension is an independent risk factor for worse clinical outcomes among patients hospitalized for COVID-19. In our analysis, hypertension was shown to have a significant association with in-hospital mortality, respiratory failure, ICU admission, severe/critical COVID-19 at nadir, and neurologic complications.
Since it is the most common comorbidity among patients with COVID-19, several studies were done to determine the relationship between hypertension with poor clinical outcomes in this patient population. These studies were heterogeneous in their findings, with some showing a positive association [
9,
10], while others showed no association with outcomes such as mortality or severity of COVID-19 [
12‐
14]. Due to its complexity, the impact of hypertension on the COVID-19 disease course (and vice-versa) has been difficult to characterize. An early study on hospitalized patients suggested that elevated systolic blood pressure and blood pressure variability were associated with higher mortality, ICU admission, and COVID-induced heart failure [
21]. Another observational study showed a similar association but found no significant difference in outcomes among the different grades of hypertension (i.e., grade 1 hypertension versus grade 2 or 3 hypertension) [
22]. Further study needs to be done among the hypertensive population to determine if the severity of hypertension and level of control has any effect on COVID-19 clinical outcomes. Data are also scarce on comparisons of outcomes between hypertensive patients who are chronically hypertensive versus newly diagnosed.
The pathophysiologic mechanisms to explain the poorer outcomes observed in hypertensive patients with COVID-19 are also under investigation. It is suggested that chronically hypertensive patients have greater endothelial dysfunction and hypertension-mediated organ damage, increasing their susceptibility to cardiovascular complications if they are infected with COVID-19 [
23]. It is also hypothesized that hypertension and SARS-CoV-2 interact with the ACE/Angiotensin II/AT1R axis, which promotes vasoconstriction and RAAS upregulation, as well as the vasodilatory ACE2/Ang (1–7)/AT2R axis, to promote viral entry, replication, and organ damage [
24,
25]. Recent studies on hypertension and atherosclerosis have shown that immune cell infiltration and cytokine production play a role in sustaining elevated blood pressure and target organ damage [
26]. As such, the pro-inflammatory cascade brought about by COVID-19 infection may compound the existing chronic inflammation in hypertensive patients. Supporting this hypothesis, findings of a study also demonstrated that the immune cells in the airways of COVID-19 patients with hypertension exhibited inflammatory signals, which correlated with COVID-19 disease progression [
27]. To date, no studies have yet specifically explored the association of hypertension with COVID-19-related cytokine storm.
Hypertension is a well-known and prevalent risk factor for cardiovascular disease. Hypertension occurs in conjunction with several modifiable and non-modifiable factors that often cluster and work in synergy, such as in metabolic syndrome. We confirmed this clustering of comorbidities in our analysis of the Philippine CORONA Study data. Earlier studies that showed an association of hypertension with poor clinical outcomes did not consider these comorbidities, which are likely to confound the observations. In one study, hypertension alone did not affect mortality or ARDS in COVID-19, but there was an association if considered together with diabetes [
11]. In another study, neither hypertension nor diabetes mellitus affected the clinical outcomes in critically ill COVID-19 patients [
12]. We adjusted our regression and time-to-event analyses for these predetermined confounders and found that the positive association of hypertension with poor outcomes remains significant.
The burden of hypertension and its interaction with COVID-19 is not only limited to the comorbid itself but also the medications used to treat the condition. In particular, animal studies have shown that renin–angiotensin–aldosterone system (RAAS) inhibitors increase the expression of ACE2 receptors, which constitute one of the initial steps in COVID-19 viral entry into cells [
28]. These findings led to succeeding studies investigating the association of using these anti-hypertensive medications on clinical outcomes, such as worsening severity and mortality. Although initially thought to increase the risk of COVID-19 infection, using RAAS inhibitors did not significantly increase the risk of infection or mortality from COVID-19 in several observational studies [
29‐
31]. A large study involving 16866 cases of COVID-19 in the United Kingdom showed that using RAAS blockers, calcium channel blockers, and thiazides among hypertensives were associated with a lower risk of infection and no effect on mortality [
32]. More recently, a randomized clinical trial BRACE CORONA involving 659 patients hospitalized for COVID-19 showed that continuing RAAS inhibitors during COVID-19 hospitalization versus discontinuing them did not affect days alive and out-of-hospital in 30 days, mortality, cardiovascular death, or COVID-19 progression [
33]. The European Society of Cardiology, Italian Society of Hypertension, and British Cardiovascular Society have also released their official statements on the safety of continuing RAAS inhibitors among patients who have conditions for which these are indicated [
34‐
36]. There is also a hypothesis that beta-blockers, unlike RAAS blockers, may improve outcomes in COVID-19 patients, as they were found to reduce the expression of ACE2 receptors and interleukin-6 [
37]. In the UK study, beta-blocker use was even initially associated with higher odds of COVID-19 infection, but this effect was attenuated after adjusting for confounders. Succeeding studies on the association of different classes of anti-hypertensives with outcomes discovered no significant impact on the risk of COVID-19 infection, need for MV, and mortality [
9,
38,
39].
Currently, several therapeutics have been shown to prevent disease progression among patients with mild and moderate diseases. In phase 3 trials, antivirals nirmatrelvir–ritonavir [
40] and molnupiravir [
41] were shown to reduce the composite risk of hospitalization and 28-day mortality among symptomatic, unvaccinated adults with at least one risk factor for progression. While the nirmatrelvir–ritonavir trial included hypertension as a risk factor for progression, the molnupiravir trial did not. Our findings serve to strengthen the role of hypertension as a risk factor for COVID-19 disease progression and promote its consideration as an additional indication for prescribing these promising therapeutics.
In the Philippines, a sizeable proportion of the population has hypertension, ranging from 19.2% among adults 20–59 years of age to 35% for those aged 60 years and above [
8]. Based on previous studies and confirmed by our findings, individuals with hypertension are at significantly higher risk of mortality and poor clinical outcomes once infected with COVID-19. Since they are at risk for disease progression requiring mechanical ventilation and intensive care, hypertensive patients with COVID-19 represent a vulnerable population. Further study must be done to determine which subsets of the hypertensive population, if any, are most at risk and if they would benefit from intensified protective measures, such as vaccine prioritization and antiviral distribution.
Our data were limited and did not include hypertension-related characteristics, such as chronicity, severity of hypertension, level of blood pressure control, and anti-hypertensives used. Data on whether hypertension was primary or secondary were also unavailable. These factors may affect the pathophysiology of COVID-19 through worsened atherosclerosis, endothelial dysfunction, and target organ damage such as myocardial injury.
Acknowledgements
We would like to thank the Philippine CORONA Study Group Investigators and sites: Asian Hospital and Medical Center, Muntinlupa City(Corina Maria Socorro A. Macalintal, MD; Joanne B. Robles, MD), Baguio General Hospital and Medical Center, Baguio City (Paulo L. Cataniag, MD; Manolo Kristoffer C. Flores, MD, MBA), Cagayan Valley Medical Center, Tuguegarao City (Noreen Jhoanna T. Trinidad, MD), Capitol Medical Center, Quezon City (Dan Neftalie A. Juangco, MD; Giuliani Renz G. Paas, MD), Cardinal Santos Medical Center, San Juan City (Audrey Marie U. Chua, MD, Valmarie S. Estrada, MD, Philip Rico P. Mejia, MD, Therese Franz B. Reyes, MD), Chong Hua Hospital, Cebu City (Maria Teresa A. Cañete, MD; Ferdinand Renfred A. Zapata, MD), De La Salle University Medical and Health Sciences Institute, Dasmariñas City, (Franko Eugenio B. Castillo, MD; Romulo U. Esagunde, MD; Jean B. Gantioque, MD), Dr. Jose N. Rodriguez Memorial and Sanitarium Hospital, Caloocan City (Maritoni C. Abbariao, MD; Geramie M. Acebuque, MD), Dr. Pablo O. Torre Memorial Hospital, Bacolod City (Evram V. Corral, MD), East Avenue Medical Center, Quezon City (Marian Irene C. Escasura, MD; Marissa T. Ong, MD), Jose B. Lingad Memorial Regional Hospital, City of San Fernando (Arnold Angelo M. Pineda, MD; Khasmeen D. Aradani, MD), Jose R. Reyes Memorial Medical Center, Manila (Joseree-Ann S. Catindig, MD; Mark Timothy T. Cinco, MD; Mark Erving H. Ramos, MD), Lung Center of the Philippines, Quezon City (Romulus Emmanuel H. Cruz, MD; Marita B. Dantes, MD; Norberto A. Francisco, MD; Rosalia A. Teleg, MD), Makati Medical Center, Makati City (Krisverlyn B. Bellosillo, MD; Jean Paolo M. Delfino, MD; Cid C. Diesta, MD; Rosalina B. Espiritu-Picar, MD; Julie Anne V. Gamboa, MD; Cara Camille M. Matute, MD; Franzelle P. Padilla, MD; John Joshua Q. Punsalan, MD), Manila Doctors Hospital, Manila (Ma. Epifania V. Collantes, MD; Charmaine B. Que, MD; Hanifa A. Sampao, MD; Maxine Camela S. Sta. Maria, MD), Medical Center Manila, Manila (Marita M. Fuentes, MD; Jennifer Justice F. Manzano, MD; Rizza J. Umali, MD), New Era General Hospital, Quezon City (Marc Conrad C. Molina, MD), Northern Mindanao Medical Center, Cagayan de Oro City (Hazel Claire Minerva-Ang, MD; Arturo F. Surdilla, MD; Loreto P. Talabucon Jr., MD; Natasha F. Wabe, MD), Quirino Memorial Medical Center, Quezon City (Maria Victoria G. Manuel, MD; Al Inde John A. Pajantoy, MD; Josephine Cecilia V. Roque, MD; Paul Emmanuel L. Yambao, MD), Ospital ng Makati, Makati City (Christian Paul B. Banday, MD; Chritopher C. Cipriano, MD; Nehar A. Pangandaman, MD; Avery Gail C. Wasil, MD), Perpetual Succour Hospital, Cebu City (Elrey P. Inocian, MD; Jarungchai Anton S. Vatanagul, MD), Philippine General Hospital, Manila (Almira Doreen Abigail O. Apor, MD; Carissa Paz C. Dioquino, MD), Philippine Heart Center, Quezon City (Prinz Andrew M. Dela Cruz, MD; Maricar P. Yumul, MD), Research Institute for Tropical Medicine, Muntinlupa City (Ma. Alma E. Carandang-Concepcion, MD), San Juan De Dios Educational Foundation Inc. Hospital, Pasay City (Ma. Caridad V. Desquitado, MD; Carl Kevin L. Julao, MD), San Lazaro Hospital, Manila(Dante P. Bornales, MD), Southern Isabela Medical Center, Santiago City (Generaldo D. Maylem, MD; Mark Joseph F. Cuntapay, MD), Southern Philippines Medical Center, Davao City (Annabelle Y. Lao-Reyes, MD; Aileen Mae B. Lee, MD; Nadia O. Manlegro, MD; Dave Mar L. Pelere, MD), St. Luke’s Medical Center—Global City, Taguig City(Lina C. Laxamana, MD; Diana-Lynn S. Que, MD; Jeryl Ritzi T. Yu, MD), St. Luke’s Medical Center, Quezon City (Ma. Socorro C. Martinez, MD; Alexandria E. Matic, MD; John Angelo Luigi S. Perez, MD), The Medical City, Pasig City (Glenn Anthony A. Constantino, MD; Aldanica R. Olano, MD; Liz Edenberg P. Quiles, MD; Artemio A. Roxas, Jr., MD; Jo Ann R. Soliven, MD; Michael Dorothy Frances Montojo-Tamayo, MD), University of Santo Tomas Hospital, Manila (Ma. Lourdes C. Joson, MD; Jojo R. Evangelista, MD), University of the East Ramon Magsaysay Memorial Medical Center Inc., Quezon City (Ma. Clarissa B. Nuñez, MD; Marietta C. Olaivar, MD; Dominique Q. Perez, MD), Veterans Memorial Medical Center, Quezon City (Mark Deneb O. Armeña, MD; Robert A. Barja, MD), Vicente Sotto Memorial Medical Center, Cebu City (Joshua Emmanuel E. Abejero, MD; Maritzie R. Eribal, MD), Western Visayas Medical Center, Iloilo City (Ryndell G. Alava, MD), Zamboanga City Medical Center, Zamboanga City (Muktader A. Kalbi, MD; Nasheera W. Radja, MD; Mohammad Elshad S. Sali, MD).