Etiology of Human Coronavirus HKU1 Infection in Adults
Human coronavirus HKU1 (HCoV-HKU1) infection in adults is caused by a group 2 betacoronavirus that spreads primarily through respiratory droplet transmission and contact routes, with infected symptomatic patients serving as the main infection source. 1, 2
Viral Characteristics and Classification
HCoV-HKU1 is a betacoronavirus belonging to group 2, distinct from other endemic human coronaviruses 1, 3. The virus demonstrates neurotropic potential and has been associated with new-onset psychosis (OR 1.3) in some cases 3. The virus infects human respiratory epithelial cells and can be detected in both respiratory and gastrointestinal specimens 4.
Transmission Mechanisms
The primary mode of transmission occurs through respiratory droplets from infected individuals, with contact transmission serving as a secondary route. 1 Key transmission characteristics include:
- Infected symptomatic patients represent the main infection source 1
- Respiratory secretions contain viable virus that spreads via droplet and contact routes 1
- The virus can be shed in both nasopharyngeal specimens and stool samples 4
- Asymptomatic or persistent infection may occur in immunocompromised patients 4
Epidemiological Patterns
HCoV-HKU1 demonstrates specific seasonal and demographic patterns:
- Peak circulation occurs during winter months, with cases extending into spring and early summer 5
- The virus accounts for approximately 1.6% of adult respiratory infections requiring medical evaluation 2
- Detection rates range from 0.3% to 4.4% in screened populations 4, 5
- Multiple genotypes can cocirculate simultaneously during epidemic periods 5
Risk Factors for Infection in Adults
Adults with underlying respiratory conditions and immunosuppression face higher risk of HCoV-HKU1 infection. 2 Specific risk factors include:
- History of smoking (85% of infected adults in one series) 2
- Use of inhaled corticosteroids (38% of cases) 2
- Underlying chronic respiratory disease 2
- Immunocompromised states, including X-linked agammaglobulinemia 4
Clinical Pitfalls and Caveats
A critical pitfall is the frequent administration of antibiotics (62% of cases) despite viral etiology, highlighting the importance of viral testing. 2 Additional considerations include:
- Coinfection with other respiratory pathogens occurs in approximately 15% of cases, most commonly with influenza A 2
- The virus can cause severe disease requiring intensive care (29% of hospitalized adults) and supplemental oxygen (71% of hospitalized cases) 2
- Gastrointestinal symptoms occur in 38% of adult cases, which may mislead initial diagnostic assessment 2
- The virus demonstrates year-round circulation rather than strict seasonal restriction, unlike some other coronaviruses 5, 6
Median hospitalization duration is 5 days for adults requiring admission, with mortality documented in severe cases where no other pathogen was identified. 2