Background: Secondary attack rate is the proportion of primary contacts that develop infection or symptom within one incubation period after contact with an index case. The secondary attack rate will help in studying and understanding the transmission dynamics of infectious diseases. As coronavirus disease (COVID-19) is a novel disease which has resulted in a pandemic, understanding the transmission dynamics is very important for strengthening preventive measures.Methods: The present cross-sectional study was conducted to estimate the secondary attack rate among primary contacts of COVID-19 cases admitted in a tertiary care centre in Northern Kerala. Secondary attack rate was calculated as the percentage of primary contacts that tested positive for COVID-19 with RT-PCR test within 14 days of exposure.Results: Secondary attack rate was found to be 5.88%, secondary clinical attack rate 2.35% and secondary infection rate 3.53%. Among those contacts that developed disease, 80% were household contacts.Conclusions: Secondary attack rate was 5.88% and household contacts were the majority to get the disease.

Background: The first case of COVID-19 in Kannur district was reported in first week of March, 2020. An elderly female with multiple co-morbidities and confined to house for many years was detected to be positive for SARS-CoV-2 on third week of May, 2020. She neither had relevant travel history nor was a contact of any confirmed COVID-19 case. A special investigation team was assigned to identify the source of infection.Methods: Index case's residential premises and the concerned local Primary Health Centre (PHC) were visited to get an idea about the background details of the index case. The team members participated in focus group discussions for decision making and reviewing steps involved in the process of investigation. Data collection was done mainly through phone interviews using an open- ended questionnaire. Data collected from family members, relatives, neighbours and local leaders were compiled systematically and summarized descriptively to reach a hypothesis.Results: Rigorous contact tracing of index case and appropriate testing of the contacts were done. Interstate truck drivers bringing fish from outside Kerala, who used to deliver fish to the index case’s house were identified as the source of infection. These truck drivers used to deliver fish in the local fish market also. The district administration was immediately alerted and fish market was disinfected and closed which prevented further mushrooming of cases.Conclusions: Early epidemiological investigation for source identification and elucidation of chain of disease transmission is crucial to clamp down the outbreak efficiently.

Background: Coronavirus disease 19 (COVID-19) started as pneumonia of unknown cause detected first in Wuhan, China in December 2019 and spread as a pandemic affecting more than 200 countries worldwide. The most common symptoms of COVID-19 are fever, dry cough, breathing difficulty and tiredness. The median incubation period is about 5 days as per current understanding. The present study was done to estimate the median incubation period of COVID-19 cases admitted in a tertiary care center in north Kerala.Methods: This cross-sectional study included COVID-19 cases admitted in a tertiary care center during three months study period.Results: The median incubation period of COVID-19 was estimated to be 4 days (interquartile range 7). It was also found that females, those persons with comorbidities and those who got infected by local transmission had a longer mean incubation period compared to males, those without comorbidities and imported cases, respectively.Conclusions: The median incubation period of COVID 19 was estimated to be 4 days. Factors like presence of comorbidities, gender, type of transmission were found to affect incubation period, but further studies are needed to have a thorough understanding.