A study of COVID-19 in the quarantined Italian town of Vò, where most of the population was tested, reveals the importance of asymptomatic cases.
The authors of the new research, from the University of Padova and at Imperial College London, published today in Nature, suggest asymptomatic or pre-symptomatic people are an important factor in the transmission of COVID-19. They also argue that widespread testing, isolating infected people, and a community lockdown effectively stopped the outbreak in its tracks.
Our research shows that testing of all citizens, whether or not they have symptoms, provides a way to manage the spread of disease and prevent outbreaks getting out of hand. Professor Andrea Crisanti
The town of Vò, with a population of nearly 3,200 people, experienced Italy’s first COVID-19 death on 21 February 2020. The town was put into immediate quarantine for 14 days. During this time, researchers tested most of the population for infection of SARS-CoV-2, the virus that causes COVID-19, both at the start of the lockdown (86 percent tested) and after two weeks (72 percent tested).
The testing revealed that at the start of the lockdown, 2.6 percent of the population (73 people) were positive for SARS-CoV-2, while after a couple of weeks only 1.2 percent (29 people) were positive. At both times, around 40 percent of the positive cases showed no symptoms (asymptomatic). The results also show it took on average 9.3 days (range of 8-14 days) for the virus to be cleared from someone’s body.
None of the children under ten years old in the study tested positive for COVID-19, despite several living with infected family members. This is in contrast to adults living with infected people, who were very likely to test positive.
As a result of the mass testing any positive cases, symptomatic or not, were quarantined, slowing the spread of the disease and effectively suppressing it in only a few short weeks.
A model for suppressing transmission
Co-lead researcher Professor Andrea Crisanti, from the Department of Molecular Medicine of the University of Padua and the Department of Life Sciences at Imperial, said: “Our research shows that testing of all citizens, whether or not they have symptoms, provides a way to manage the spread of disease and prevent outbreaks getting out of hand. Despite ‘silent’ and widespread transmission, the disease can be controlled.”
The results of the mass testing programme in Vò informed policy in the wider Veneto Region, where all contacts of positive cases were offered testing. “This testing and tracing approach has had a tremendous impact on the course of the epidemic in Veneto compared to other Italian regions, and serves as a model for suppressing transmission and limiting the virus’ substantial public health, economic and societal burden,” added Professor Crisanti.
As well as identifying the proportion of asymptomatic cases, the team also found that asymptomatic people had a similar ‘viral load’ – the total amount of virus a person has inside them – as symptomatic patients.
Viral load also appeared to decrease in people who had no symptoms to begin with but later developed symptoms, suggesting that asymptomatic and pre-symptomatic transmission could contribute significantly to the spread of disease, making testing and isolating even more important in controlling outbreaks.
Early identification and timely isolation
Co-lead researcher Dr Ilaria Dorigatti, from the MRC Centre for Global Infectious Disease Analysis, Jameel Institute (J-IDEA), at Imperial College London, said: "The Vò study demonstrates that the early identification of infection clusters and the timely isolation of symptomatic as well as asymptomatic infections can suppress transmission and curb an epidemic in its early phase. This is particularly relevant today, given the current risk of new infection clusters and of a second wave of transmission.
"There are still many open questions about the transmission of the SARS-CoV-2virus, such as the role of children and the contribution of asymptomatic carriers to transmission. Finding answers to these questions is crucial to identifying targeted and sustainable control strategies to combat the spread of SARS-CoV-2 in Italy and around the world."
The en mass participation of the Vo’ population to this study has given us the opportunity to better understand the transmission of this virus and how to avoid future infections. Dr Elisa Franchin
Professor Enrico Lavezzo, from the Department of Molecular Medicine at the University of Padua, said: "The result concerning asymptomatic carriers is key. We took a picture of the Vò population and found that about half of the population testing positive had no symptoms at the time of testing and some of them developed symptoms in the following days. This tells us that if we find a certain number of symptomatic people testing positive, we expect the same number of asymptomatic carriers that are much more difficult to identify and isolate.
"The fact that the viral load is comparable between symptomatic and asymptomatic carriers means even asymptomatic infections have the potential to contribute to transmission, as some of the reconstructed chain of transmission obtained from the detailed contact tracing conducted in ;Vò confirmed.
"On the one hand, it is likely that a symptomatic infection transmits large quantities of virus, for example via coughing, but it is also reasonable to think that symptoms may induce a person with a symptomatic infection to stay at home, limiting the number of contacts and hence the transmission potential. On the other hand, someone with an asymptomatic infection is entirely unconscious of carrying the virus and, according to their lifestyle and occupation, could meet a large number of people without modifying their behaviour."
Co-first author Dr Elisa Franchin, from the Department of Molecular Medicine of the University of Padua, said: “This work highlights the efficacy of the containment strategies implemented since the finding of the first positive patient in the town of Vò. From a technical perspective, this work has been possible thanks to the most advanced diagnostic technologies that we had available and to the work of a large number of people with different skills: from nurses to clerks, technicians, biologists and medical doctors. The en mass participation of the Vo’ population to this study has given us the opportunity to better understand the transmission of this virus and how to avoid future infections.”
This research was funded by the Veneto Region, Wellcome Trust, Royal Society, the European Union's Horizon 2020 research and innovation programme, the UK Medical Research Council (MRC) and the UK Department for International Development (DFID) under the MRC/DFID Concordat agreement, the EDCTP2 programme supported by the European Union and the Abdul Latif Jameel Foundation.
‘Suppression of a SARS-CoV-2 outbreak in the Italian municipality of Vo’’ by Enrico Lavezzo et al is published in Nature.
Top image: Professor Stefano Merigliano testing a child. Credit: Professor Andrea Crisanti
Article text (excluding photos or graphics) © Imperial College London.
Photos and graphics subject to third party copyright used with permission or © Imperial College London.
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Utafiti wa COVID-19 katika mji wa Italia wa Volo, ambapo idadi kubwa ya watu walichunguzwa, unafunua umuhimu wa kesi zisizo na dalili. Watafiti kutoka Chuo Kikuu cha Padua na Chuo Kikuu cha Imperial London, walichapisha katika jarida la Nature, wanasema kuwa watu wasio na dalili au walio na dalili za ugonjwa huo ni sababu muhimu ya kuambukizwa kwa COVID-19. "Wanasema pia kwamba upimaji wa wingi, kutenganisha watu walioambukizwa, na kufungwa kwa jamii kwa ufanisi kulisimamisha mlipuko katika nyimbo zake. """ Utafiti wetu unaonyesha kwamba kupima wananchi wote, iwe wana dalili au la, hutoa njia ya kusimamia kuenea kwa ugonjwa na kuzuia milipuko kutoka kwa udhibiti. Mji wa Volo, wenye idadi ya watu karibu 3,200, ulipata kifo cha kwanza cha COVID-19 nchini Italia mnamo Februari 21. Jiji hilo lilitengwa kwa siku 14 mara moja. Katika kipindi hicho, watafiti walifanya uchunguzi wa watu wengi kwa virusi vya SARS-CoV-2 vinavyosababisha COVID-19, wakati wa kuanza kwa kufungwa kwa nchi (86% walichunguzwa) na baada ya wiki mbili (72% walichunguzwa). Uchunguzi huo ulifunua kwamba mwanzoni mwa kufungwa kwa nchi, asilimia 2.6 ya watu (watu 73) walikuwa na virusi vya SARS-CoV-2, wakati baada ya wiki chache asilimia 1.2 tu (watu 29) walikuwa na virusi hivyo. Katika kipindi hicho, asilimia 40 ya wagonjwa hao hawakuwa na dalili zozote. Matokeo ya uchunguzi huo yanaonyesha kuwa ilichukua wastani wa siku 9.3 (kati ya siku 8-14), kwa virusi hivyo kuondolewa kwenye mwili wa mtu. Hakuna mtoto yeyote chini ya umri wa miaka kumi aliyepatikana na COVID-19 licha ya kuwa na watu kadhaa wa familia walioambukizwa. Hii ni tofauti na watu wazima wanaoishi na watu walioambukizwa, ambao walikuwa na uwezekano mkubwa wa kupima chanya. Kwa sababu ya upimaji wa wingi, kesi zozote za chanya, zenye dalili au zisizo na dalili, ziliwekwa kwa karantini, kupunguza kuenea kwa ugonjwa na kuuzuia kwa ufanisi katika wiki chache tu. "Mtaalamu Andrea Crisanti, kutoka Idara ya Tiba ya Molekuli ya Chuo Kikuu cha Padua na Idara ya Sayansi ya Maisha ya Imperial, alisema: ""Utafiti wetu unaonyesha kwamba kupima raia wote, iwe wana dalili au la, hutoa njia ya kusimamia kuenea kwa ugonjwa na kuzuia milipuko kutoka kwa mkono." "Licha ya ""kutokuwa na sauti"" na maambukizi ya kuenea, ugonjwa unaweza kudhibitiwa. "" Matokeo ya mpango wa upimaji wa wingi huko Vò yalijulisha sera katika Mkoa mkubwa wa Veneto, ambapo mawasiliano yote ya kesi nzuri yalipewa upimaji." "Mkakati huu wa kupima na kufuatilia umekuwa na athari kubwa kwa mwendo wa janga huko Veneto ikilinganishwa na mikoa mingine ya Italia, na hutumika kama mfano wa kukandamiza maambukizi na kupunguza virusi, mzigo mkubwa wa afya ya umma, kiuchumi na kijamii,"" alisema Profesa Crisanti." Pamoja na kutambua uwiano wa kesi zisizo na dalili, timu hiyo pia iligundua kuwa watu wasio na dalili walikuwa na'mzigo wa virusi' sawa - jumla ya virusi ambavyo mtu ana ndani yao - kama wagonjwa wenye dalili. "Watu ambao hawakuwa na dalili za ugonjwa huo lakini baadaye walipata dalili, walionyesha kwamba ""kuambukizwa bila dalili na kabla ya dalili"" kunaweza kuchangia sana kuenea kwa ugonjwa huo, na kufanya upimaji na kutengwa kuwa muhimu zaidi katika kudhibiti milipuko." "Mtaalamu wa utafiti Ilaria Dorigatti, kutoka Kituo cha MRC cha Uchambuzi wa Magonjwa ya Kuambukiza Ulimwenguni, Taasisi ya Jameel (JIDEA), Imperial College London, alisema: ""Utafiti wa VOA unaonyesha kuwa utambulisho wa mapema wa makundi ya maambukizi na kutengwa kwa wakati wa maambukizi ya dalili na asymptomatic inaweza kukandamiza na kuzuia maambukizi katika hatua yake ya mapema." Hii ni muhimu hasa leo, kwa kuzingatia hatari ya sasa ya makundi mapya ya maambukizi na wimbi la pili la maambukizi. "Bado kuna maswali mengi ya wazi juu ya maambukizi ya virusi vya SARS-CoV-2, kama vile jukumu la watoto na mchango wa wabebaji wasio na dalili kwa maambukizi.""" "Kupata majibu ya maswali haya ni muhimu kwa kutambua mikakati ya udhibiti wa lengo na endelevu ili kupambana na kuenea kwa SARS-CoV-2 nchini Italia na ulimwenguni kote. """ Ushiriki wa wingi wa idadi ya watu wa Vo kwa utafiti huu umetupa fursa ya kuelewa vizuri uhamisho wa virusi hivi na jinsi ya kuepuka maambukizi ya baadaye. "Elisa Franchin, profesa wa Enrico Laval, kutoka Idara ya Tiba ya Molekuli katika Chuo Kikuu cha Padua, alisema: ""Hatua hii ya kuambukiza ni muhimu." "Tuliangalia idadi ya watu wa VOA na tukagundua kwamba karibu nusu ya watu waliopima kuwa na virusi vya corona hawakuwa na dalili wakati wa kupima na wengine wao walipata dalili katika siku zilizofuata. """ "Hii inatuambia kwamba ikiwa tutapata idadi fulani ya watu wenye dalili, tunatarajia idadi sawa ya wabebaji wasio na dalili ambao ni vigumu zaidi kutambua na kutenganisha.""" "Ukweli kwamba mzigo wa virusi ni sawa kati ya wabebaji wenye dalili na wasio na dalili unamaanisha hata maambukizi yasiyo na dalili yana uwezo wa kuchangia maambukizi, kama baadhi ya mlolongo wa maambukizi uliorekebishwa uliopatikana kutoka kwa kufuatilia mawasiliano ya kina uliofanywa katika ""Vox.""" "Kwa upande mmoja, ni uwezekano kwamba maambukizi ya dalili husambaza kiasi kikubwa cha virusi, kwa mfano kupitia kikohozi, lakini pia ni busara kufikiri kwamba dalili zinaweza kusababisha mtu mwenye maambukizo ya dalili kukaa nyumbani, kupunguza idadi ya mawasiliano na hivyo uwezekano wa maambukizi. """ Kwa upande mwingine, mtu aliye na maambukizi yasiyo na dalili hajui kabisa kuwa ana virusi hivyo, na kulingana na mtindo wake wa maisha na kazi, anaweza kukutana na idadi kubwa ya watu bila kubadilisha tabia yake. "Mwandishi mwenza wa kwanza, Dk Elisa Franchin, kutoka Idara ya Tiba ya Molekuli ya Chuo Kikuu cha Padua, alisema: ""Kazi hii inaangazia ufanisi wa mikakati ya kuzuia iliyotumika tangu kupatikana kwa mgonjwa wa kwanza mzuri katika mji wa Volo." Kwa upande wa kiufundi, kazi hii imefanywa kwa sababu ya teknolojia za kisasa za utambuzi ambazo tulikuwa nazo na kwa kazi ya idadi kubwa ya watu wenye ujuzi tofauti: kutoka kwa wauguzi hadi wafanyikazi, wataalamu wa teknolojia, wataalamu wa biolojia na madaktari. "Uchunguzi huu umefadhiliwa na Mkoa wa Veneto, Wellcome Trust, Royal Society, mpango wa utafiti na uvumbuzi wa Umoja wa Ulaya wa Horizon 2020, Baraza la Utafiti wa Matibabu la Uingereza (MRC), na Idara ya Maendeleo ya Kimataifa ya Uingereza (DFID) chini ya makubaliano ya MRC-CDID, mpango wa EDCTP2 unaoungwa mkono na Umoja wa Ulaya na Msingi wa Abdul Latif Jameel.""" "Uchunguzi wa ""SARS-CoV-2"" katika mji wa Italia wa Vo, uliofanywa na Enrico Lavezzoli na wenzake, ulichapishwa katika jarida la Nature." Picha ya juu: Profesa Stefano Merigliano akimchunguza mtoto. "Mwandishi Andrea Crisanti, Mkurugenzi wa Chuo Kikuu cha Imperial College London, alisema: ""Mwanzoni mwa miaka ya 1990 kulikuwa na mabadiliko makubwa katika elimu." Picha na picha zinazohusika na haki za uchapaji za mtu wa tatu zinazotumiwa kwa ruhusa au © Chuo cha Imperial London. Kuondoka maoni: Maoni yako yanaweza kuchapishwa, kuonyesha jina lako kama unavyotoa, isipokuwa ukiomba vinginevyo. Maelezo yako ya mawasiliano hayatapatikana kamwe.