Objectives:
Are gastrointestinal symptoms with COVID-19 associated with a higher risk of acute respiratory distress syndrome and mortality?

Study design:
This review article included 4 studies.

Results and conclusions:   
The investigators found no association between gastrointestinal symptoms with COVID-19 and mortality risk [pooled odds ratio = 0.91, 95% CI = 0.49 to 1.68, I2 = 0%].  

Objectives:
The prevalence of co-infection of hepatitis B virus (HBV) and human immunodeficiency virus (HIV) is high and increases risk of hepatitis B chronicity and mortality. Despite guidelines for HIV-infected patients to be immunized against HBV, the immunogenicity of the HBV vaccination in HIV-infected patients is lower than that in the HIV-seronegative population. Therefore, this review article has been conducted.

Objectives:
Is there an association between physical distancing interventions and reductions in incidence of coronavirus disease 2019 (covid-19) globally?

Study design:
This review article included studies in 149 countries or regions.

Objectives:
Epidemiologic studies, including trials, suggest an association between potassium intake and blood pressure (BP). However, the strength and shape of this relationship is uncertain. Therefore, this review article has been conducted.

Objectives:
Is there an association between all-cause mortality of COVID-19 and age?

Study design:
This review article included all available national reports on May 7, 2020 from China, Italy, Spain, United Kingdom and New York State with a total of 611,1583 COVID-19-positive patients, of which 141,745 (23.2%) were aged ≥80 years.
The percentage of octogenarians (persons whose age are in the eighties) was different in the 5 registries, the lowest being in China (3.2%) and the highest in the United Kingdom and New York State.

Objectives:
Has oral supplementation of vitamin B (vitamins B1, B6, B12 and folic acid alone or combined) preventive effect on cognitive decline in cognitively unimpaired individuals?

Study design:
This review article included 20 RCTs, ranging from 23 to 2,919 participants per study, with a total of 12,697 participants.
8 of these 20 RCTs were deemed appropriate for the meta-analysis.

Results and conclusions:

Objectives:
Some of the symptoms of COVID-19 are fever, cough and breathing difficulty. However, the mechanism of the disease, including some of the symptoms such as the neurological and musculoskeletal symptoms, is still poorly understood. Therefore, this review article has been conducted.

Objectives:
Lymphoma etiology remains ill-defined, but immune factors seem to play a major role. The Bacillus Calmette-Guérin (BCG) vaccine, a non-specific stimulator of the cellular immune response, could influence lymphoma risk. Previous studies addressing this issue showed conflicting results. Therefore, this review article has been conducted.

Objectives:
Which are the characteristics of asymptomatic infection in the coronavirus disease 2019 (COVID-19)?

Study design:
This review article included 41 studies with a total of 50,155 patients with confirmed COVID-19.

10 included studies contain the number of pre-symptomatic patients, who were asymptomatic at screening point and developed symptoms during follow-up.

Objectives:
Evidence is mounting to indicate that cancer patients may have more likelihood of having coronavirus disease 2019 (COVID-19) but lack consistency. Therefore, this review article has been conducted.

Is cancer comorbidity (comorbidity refers to the presence of more than one disorder in the same person) associated with the risk and severe events of COVID-19?

Study design:
This review article included 38 studies comprising 7,094 patients with COVID-9.