The current study traced the transmission of COVID-19 by 201 cases including 126 male (62.7%) and 75 female (37.3%) patients. For each of the 201 patients a separate case study was conducted which included 155 pre-symptomatic and 46 asymptomatic patients. A total of 7168 individuals who met with these 201 pre-symptomatic or asymptomatic patients during a time period of 24 hours before the appearance of symptoms or confirmation of infection (mean meetings per patient = 35.66) were traced in the study for confirmation of transmission. Out of 7168 contacts 64 individuals were found to be infected with COVID-19 with a transmission rate of 0.89% (Table 1). No case of infection was observed in remaining 7104 contacting persons even after a mean duration of 84±43 days with minimum of 23 days from the date of infection confirmation in patients. Out of the total 64 infected individuals, 63 were recorded to have contraction from pre-symptomatic patients while only 1 patient was traced to acquire infection from asymptomatic patients (Figure 1). The net rate of pre-symptomatic and asymptomatic transmissions were found to be 1.12% and 0.06% respectively (Table 1). Transmission of infection was found to be very low by pre-symptomatic patients and almost singular by asymptomatic patients.
Out of the total 201 cases, 155 were symptomatic who had 5611 contact events during last 24 hours before the appearance of symptoms. Mean persons meeting a pre-symptomatic patient was calculated to be 36.20. Out of these 5611 people, 5548 (98.88%) remained uninfected even after random testing and over a mean duration of 85.32±43.5 days ranging from minimum of 24 days to maximum of 210 days, while 63 of these individuals (1.12%) were tested positive. Overall percentage of transmission by pre-symptomatic patients (1.12%) was observed to be very low (Table 1; Table 2). Time line of contact event was as follows: Out of the total 5611 persons contacting the symptomatic patients before the symptoms, 1544 persons met the patients in the period of 6 hours to 0 hour before appearance of symptoms, 1410 meetings were traced in period of 12 to 6 hours, 1285 in period of 18 to 12 hours and 1372 meeting were traced in period of 24 to 18 hours before appearance of symptoms in patients. Sixty two (62) of the 63 transmissions (98.4%) were traced in the period of 0-6 hours before appearance of symptoms while 1 transmission (1.6%) was traced in the meetings during 6 to 12 hours before appearance of symptoms (Table 2). So, majority of the transmission events (98.4%) occurred in the meetings just before the appearance of symptoms while very rare transmission occurred in the meetings before 6 hours of appearance of symptoms or more (Table 2). The transmission rate was calculated to be about 4% during 0-6 hours before appearance of symptoms while it was only 0.02% in contacts before 6 hours to 24 hours of the symptoms (Table 2). The risk of getting infection from a pre-symptomatic patient before 6 hours or more of from onset of symptoms is very rare.
A total of 46 out of 201 positive cases never developed any disease symptom in the study even after a mean duration of 82.74±42.5 days ranging from minimum 23 days to maximum 180 days after tested positive. These patients were designated as asymptomatic and a total of 1557 persons were traced who had meetings with these 46 patients before they were tested positive. Out of these 1557 individuals meeting the asymptomatic patients during a mean time period of 24 hour before tested positive, only 1 person was tested positive. Interestingly, this individual who had 2 days of meeting developed mild symptoms of COVID-19 just 3 days after the meeting. This person was the brother of an asymptomatic patient and met the patient approximately about 8 hours before the appearance of symptoms in the patient. All of other traced persons (1556 out of 1557) remained asymptomatic throughout the study and were never tested positive. The transmission rate by asymptomatic patients was found to be 0.06% (Table 2).
Some selected case reports
Separate case study was conducted for each of the 155 pre-symptomatic and 46 asymptomatic positive patients. Here we discuss 4 pre-symptomatic cases and 4 asymptomatic cases as example selected out of total 201 cases (Table 3).
Case 1: Symptomatic, transmission not traced: A 45 years old male working as a labor in a floor mill returned to work from his home town after Eid-ul-Fitr holidays on May 29 and met 42 co-workers. He has been living there for about 30 hours in shared living area mess and lavatory with all of 42 co-workers. After about 27 hours, he expressed symptoms which a roommate of him identified as of COVID-19 and informed the hospital officials. The patient was carried and admitted to the hospital where he was tested positive and stayed for 19 days before complete recovery. Meanwhile, all 42 contact persons were kept in quarantined for 14 days and a random testing was carried out in which 25 of them were tested on day 7. All the 25 were found negative on day seven and none of those 42 individuals showed any symptom after day 14. Even after 150 days of their meeting with the patient, none of the persons was found infected. The transmission rate was 0% in this case (Table 3).
Case 2: Symptomatic, transmission not traced: A 21 year old male student from a village near Rawalakot carried infection from some patient in Rawalpindi and got symptoms appeared on the morning of August 1, 2020, just a day after Eid-ul-Adha. In previous 24 hours, 32 persons were traced to meet him without any precautionary measures including his family members and relatives. Early in the morning of the day next to the Eid-ul-Adha, he met with his father, mother, sister, father's sister and 3 male cousins just before the appearance of fever. After the appearance of fever, he quarantined himself. He was brought to the hospital next day where he was found positive for COVID-19 on PCR test and got hospitalized. . All the 32 individuals having close contact with him were kept in isolation immediately and 21 of them were selected randomly for test after 8 days. All tested persons including the patients family members were found negative and non of the all 32 showed any symptom after 14 days of contact and even after 70 days (on date of data collection). The patient recovered and was discharged from hospital after 12 days. Transmission rate in this case was 0% in this case (Table 3).
Case 3: Symptomatic, transmission traced: The 3rd selected case was a 66 years old male who showed symptoms on July 8, 2020 and found positive on PCR test. Just before the appearance of symptoms, on the same day, he visited a total of his 56 relatives and family members residing in Rawalakot and had intimate contact history. At about 9 pm, he felt fever and chest pain which became severe until the next morning and he was brought to the hospital where he was tested positive for COVID-19 and got admitted. After 22 days of hospital stay, he recovered and was discharged from the hospital. All the 56 meeting persons were quarantined themselves at home and 28 of them went for a PCR test. One of the meeting persons developed symptoms after 9 days and also tested positive while 27 of the tested persons were negative. Except for one positive and symptomatic person, no meeting person showed symptoms or tested positive. The transmission frequency was calculated to be 1.8% in this case (Table 3).
Case 4: Symptomatic, transmission traced: The 4th selected case was a female of 47 years old in Hajira, district Poonch AJK. She probably got the infection during a hospital visit. She was at home on June 15 and 16, where she met many relatives and family members before and during the appearance of symptoms on June 16, out of which 27 were traced. The patient was tested positive and recovered after 16 days of hospitalization. All the 27 contacted persons isolated themselves and 11 of the close relatives were tested for COVID-19. Among the close relatives remaining with patient even at the time of appearance of symptoms, two (2) daughters and husband of the patient were tested positive. However, both of the daughters never developed symptoms while husband become symptomatic after only 2 days of the patient. Remaining 24 persons did not develop any symptom after day 14 and even after 84 days of contact. The rate of transmission in this case was calculated to be 11.1% (Table 3).
Case 5: Asymptomatic, transmission not traced: A 29 year old male was found positive when tested after having a meeting with COVID-19 patient and immediately kept in quarantine center for 14 days. Fifty four (54) contacts were traced on the day he got tested for COVID-19. who all of them later isolated themselves at their homes. After 14 days, neither the positive tested person, nor any of the 54 meeting persons had any symptom. For more confirmation, 13 of the meeting persons were randomly tested but all of them were found negative in PCR test. The positive case turned to be negative in his test after the end of quarantine period on day 15. This case was designated as an asymptomatic patient and no infection transmission was traced by him even after 140 days (Table 3).
Case 6: Asymptomatic, transmission not traced: In this case, a 27 years old female was tested because she was living with her husband who was symptomatic and was tested positive. The female did not have any symptom but was found positive for COVID-19. She and 37 of her relatives who have met her recently before and during test were quarantined at their homes for 14 days where they remained asymptomatic. Moreover, 13 of the persons who were in close contact to the case were tested after a week but they all were negative. All the 37 contacting persons along with the case never developed any of the COVID-19 symptoms even after 130 days. The transmission frequency in this case was 0% (Table 3).
Case 7: Asymptomatic, transmission not traced: A 50 year old school teacher was found positive during random testing on September 12, 2020. He was kept in quarantine at home immediately and 26 persons meeting him without full precautionary measures before the test were traced and restricted to their home in isolation. After a week, 8 of the family members and relatives who met him with close contact were tested. All the tested persons were negative and none of the 26 meeting persons showed any symptom after day 14 and even after day 28 (Date of data collection). The transmission frequency in this case was found to be 0% (Table 3).
Case 8: Asymptomatic, transmission traced: This was the only asymptomatic case through which a probable transmission was traced. The patient was a 39 years old businessman who was tested positive on July 14, 2020. He was quarantined for 14 days during which he did not showed any symptoms and again tested after quarantine period in which he was negative. Before his test, he met 23 persons including 6 of his family members, who quarantined themselves on their homes after the test. All 6 of the patient's family members and 3 close relatives were selected for test after 5 days in which his 34 years old brother was tested positive but remained asymptomatic throughout the quarantine period. None of the 23 meeting persons showed any symptom even after 88 days of their meeting. The transmission rate was found to be 4.3% in this case (Table 3).