Electronic-nose had been used to diagnose other infectious lung diseases, such as tuberculosis. Universitas Gadjah Mada has developed an electronic-nose device which is easy-to-use, portable, and can be manufactured at a low price. Here the investigators test the electronic-nose to diagnose COVID-19 in Indonesia.

The validation of device is conducted to 43 confirmed COVID-19 patients and 40 confirmed COVID-19 negative patients from Bhayangkara Hospital, RSLKC Bambalipuro in Yogyakarta Special Region, Indonesia.

Afterwards, patients with symptoms suggesting COVID-19 will be recruited using multicentre consecutive sampling. The minimum number of participants required is 1460 subjects. The study use a triple-blind design where the research subjects, breath sample takers, and sample examiners did not know the results of each sampling that had been done. The final data processor was also blinded to the results of nose and throat swabs. The breath sampling data is saved in graphic form which interpretation will be carried out later by the data processor at the final stage.

This study population involve children and adults who come to the COVID-19 outpatient clinic in each participating hospital with a diagnosis of suspected COVID-19 infection. All patients remain in the setting under medical service in accordance with the standard operating procedure (SOP) and clinical practice guidelines (CPG) protocols for handling patients with suspected COVID-19. The patients underwent nasal and oropharyngeal swabs according to the COVID-19 outpatient CPG.

The participants will be asked about symptoms that they have, such as fever, fatigue, dry cough, stuffy/ runny nose, sore throat, myalgia, shortness of breath, and diarrhea. Afterwards, they will be asked to breathe normally using a mask for 2 times, then inhale and exhale in a forced expiratory volume to an air collecting bag that later is connected to the e-nose machine via a HEPA-filter. The performance of breath test will be compared with the performance of symptoms with the reference of RT-PCR results. In addition, participants' demographic and clinical data will be collected.

Inclusion Criteria:

• Patients diagnosed with COVID-19, non COVID-19, and suspected COVID-19 infection, based on the results of anamnesis, physical examination, laboratory, X-rays and rapid tests.
• Able to produce samples for RT-PCR examination.
• Agree to participate (sign informed consent). For children, informed consent are obtained from the parents. For adolescent patients, accent consent is asked.
• Patients who do not need oxygen therapy supplementation in the form of mask-type or ventilator. Patients who use oxygen supplementation with nasal cannula are still included as study participants.

Exclusion Criteria:

• Unable to breath deeply due to difficulty breathing due to complications of COVID-19 or other diseases
• The quality of the breath do not meet the standard interpretation of the instrument sensor curve (breath sampel is declared invalid).

The person who operates breath test is blinded to the results of swab. The swab taker is blinded to the result of breath sample. The patients also do not know the results of the interpretation of the breath sample. Patients will receive information on the results of the oro/ nasopharyngeal swab in accordance with the COVID-19 health service standards. The final data processor is also blinded to the results of nose and throat swabs. The breath sampling data is saved in graphic form which interpretation will be carried out later by the data processor at the final stage.