![TURIN, ITALY - FEBRUARY 28: Blood and plasma samples used for the evaluation swabs for Coronavirus in the research laboratory of the Amedeo di Savoia hospital in Turin during of the Northern Italy In The Grip Of Covid-19 Coronavirus on February 28, 2020 in Turin, Italy. (Photo by Stefano Guidi/Getty Images)](https://static.sky.it/images/skytg24/it/salute-e-benessere/approfondimenti/covid-indice-rt/hero-coronavirus-rt-getty.jpg.transform/hero-mobile/107ba54f85c52c53d3981d6278170d7aed79250b/img.jpg)
Il dato indica la probabilità di trasmissione del virus in un valore numerico che mette in rapporto gli attuali sintomatici con i possibili nuovi contagi. Quando supera l’1 comincia a destare preoccupazione: significa che i casi sono in crescita
![1208405538 TURIN, ITALY - FEBRUARY 24: Staff assigned for Coronavirus tests at the Martini hospital in Turin seen as northern Italy is locked down to try prevent the spread of Coronavirus on February 24, 2020 in Turin, Italy. (Photo by Stefano Guidi/Getty Images)](https://static.sky.it/images/skytg24/it/salute-e-benessere/approfondimenti/covid-indice-rt/01-coronavirus-rt-getty.jpg.transform/gallery-horizontal-mobile/8d21bb648b76f5f33f78be58d5a5a1b1cb23fe5e/img.jpg)
Si torna di parlare dell’indice di contagio Rt, dopo la preoccupazione per l’annuncio del ministero della Salute e dell’Istituto Superiore Sanità che hanno fatto sapere che ha di nuovo superato la soglia dell’1 al livello nazionale assestandosi all’1,01
Coronavirus, lo speciale![1228846279 ROME, ITALY - OCTOBER 02: People wearing protective masks walk around the Piazza di Spagna amid Covid-19 pandemic, on October 02, 2020 in Rome, Italy. The Lazio region President Nicola Zingaretti set an order obliging people to wear face masks in public including outdoors due to the increase of Covid-19 cases in the Lazio region. (Photo by Antonio Masiello/Getty Images)](https://static.sky.it/images/skytg24/it/salute-e-benessere/approfondimenti/covid-indice-rt/02-coronavirus-rt-getty.jpg.transform/gallery-horizontal-mobile/31cf0c957395856709c6d96a9d635dbb4dfe4e98/img.jpg)
La preoccupazione è destata dal fatto che quando l’Rt è superiore a 1 significa che il contagio è in crescita
Coronavirus, dal primo caso ai contagi: le tappe. FOTO![1209277354 TURIN, ITALY - FEBRUARY 28: Blood and plasma samples used for the evaluation swabs for Coronavirus in the research laboratory of the Amedeo di Savoia hospital in Turin during of the Northern Italy In The Grip Of Covid-19 Coronavirus on February 28, 2020 in Turin, Italy. (Photo by Stefano Guidi/Getty Images)](https://static.sky.it/images/skytg24/it/salute-e-benessere/approfondimenti/covid-indice-rt/03-coronavirus-rt-getty.jpg.transform/gallery-horizontal-mobile/107ba54f85c52c53d3981d6278170d7aed79250b/img.jpg)
L’Rt stabilisce infatti l’indice di riproduzione di una malattia, ovvero il rapporto tra i contagiati attuali e i possibili nuovi contagiati
Covid 19, Iss: in Italia Rt di nuovo sopra l'1![1206922045 A hospital employee wearing protection mask and gear shows a swab, a cotton wab for taking mouth specimen, used at a temporary emergency structure set up outside the accident and emergency department, where any new arrivals presenting suspect new coronavirus symptoms will be tested, at the Brescia hospital, Lombardy, on March 13, 2020. (Photo by Miguel MEDINA / AFP) (Photo by MIGUEL MEDINA/AFP via Getty Images)](https://static.sky.it/images/skytg24/it/salute-e-benessere/approfondimenti/covid-indice-rt/04-coronavirus-rt-getty.jpg.transform/gallery-horizontal-mobile/2cee712cbe0516fa28dbd326c3266ef09bd5c6a5/img.jpg)
Il valore Rt viene elaborato e valutato in un periodo congruo di tempo, per esempio a livello settimanale
La situazione in Italia: grafici e mappe![1206078105 A health staff checks the body temperature of a man arriving at the Juventus stadium before the Italian Serie A football match Juventus vs Inter Milan which will be played behind closed doors, in Turin on March 8, 2020. - Italy's Sports Minister called on Matrch 8 for an immediate suspension of the Serie A season due to the coronavirus outbreak that has killed 233 people in the country. (Photo by Vincenzo PINTO / AFP) (Photo by VINCENZO PINTO/AFP via Getty Images)](https://static.sky.it/images/skytg24/it/salute-e-benessere/approfondimenti/covid-indice-rt/05-coronavirus-rt-getty.jpg.transform/gallery-horizontal-mobile/81bd4117f56fac0676252a12a4601a153b3cc215/img.jpg)
Un valore diverso da R0, di cui si parlava soprattutto all’inizio di questa pandemia
La diffusione globale in una mappa interattiva![1215220207 WASHINGTON, DC - MAY 26: A medical professional administers a coronavirus test at a drive-thru testing site run by George Washington University Hospital, May 26, 2020 in Washington, DC. Dr. Deborah Birx, the lead coordinator of the White House coronavirus task force, said on Friday that the District of Columbia and its suburbs have the highest rate in the country of people testing positive for the infection. (Photo by Drew Angerer/Getty Images)](https://static.sky.it/images/skytg24/it/salute-e-benessere/approfondimenti/covid-indice-rt/07-coronavirus-rt-getty.jpg.transform/gallery-horizontal-mobile/fc0683a1c4407c32f7025c088f3758dfde9c4057/img.jpg)
R0, come Rt, indica dunque la probabilità di trasmissione per singolo contatto tra una persona infetta e una suscettibile, tenendo conto del numero dei contatti della persona infetta e della durata dell'infettività
![1214181095 A man (C) undergoes a body temperature scan as he enters the Alberto-Sordi shopping gallery on Via del Corso on May 20, 2020 in central Rome, as the country's is easing its lockdown aimed at curbing the spread of the COVID-19 infection, caused by the novel coronavirus. (Photo by Vincenzo PINTO / AFP) (Photo by VINCENZO PINTO/AFP via Getty Images)](https://static.sky.it/images/skytg24/it/salute-e-benessere/approfondimenti/covid-indice-rt/10-coronavirus-rt-getty.jpg.transform/gallery-horizontal-mobile/9291c950620bdb7cec382baf2e3c28363c678f29/img.jpg)
Bisogna tuttavia tenere conto di alcuni limiti di questo indice così utile per capire l’andamento della diffusione del virus
![1208929774 Medical workers wearing a face mask and overalls perform drive-through swabbing tests for coronavirus on people arriving by car outside the polyclinic of Alessandria, Piedmont, on April 2, 2020 during the country's lockdown aimed at curbing the spread of the COVID-19 infection, caused by the novel coronavirus. (Photo by MIGUEL MEDINA / AFP) (Photo by MIGUEL MEDINA/AFP via Getty Images)](https://static.sky.it/images/skytg24/it/salute-e-benessere/approfondimenti/covid-indice-rt/13-coronavirus-rt-getty.jpg.transform/gallery-horizontal-mobile/b45b0b53e335cbe70b9810a740be3dade0889807/img.jpg)
È per quest’ultima ragione che il valore può trovarsi a superare la soglia dell’1, anche diverse settimane dopo in cui si parla di un aumento dei casi totali
![1228306672 TOPSHOT - A woman is being scanned for body temperature as she arrives on September 2, 2020 in The Vatican, prior to the Pope's a limited public audience during the COVID-19 infection, caused by the novel coronavirus. - Pope Francis is resuming on September 2, 2020 limited public weekly audiences, six months after the head of the Catholic Church halted the practice because of the coronavirus pandemic. (Photo by Vincenzo PINTO / AFP) (Photo by VINCENZO PINTO/AFP via Getty Images)](https://static.sky.it/images/skytg24/it/salute-e-benessere/approfondimenti/covid-indice-rt/16-coronavirus-rt-getty.jpg.transform/gallery-horizontal-mobile/bc2fcb31d926bdccfad0c17bbf09cb5af30ffbb1/img.jpg)
Proprio perché effettuato solo sui casi sintomatici, l’Iss ha ammesso che l’Rt “pur rimanendo l'indicatore più affidabile a livello regionale e confrontabile nel tempo per il monitoraggio della trasmissibilità, potrebbe sottostimare leggermente la reale trasmissione del virus a livello nazionale”
![1259814639 ZURICH, SWITZERLAND - JULY 15: An employee takes a throat swab sample to test for Covid-19 at the COVID-19 Test Center at the University of Zurich during the coronavirus pandemic on July 15, 2020 in Zurich, Switzerland. Switzerland has largely lifted most of its coronavirus lockdown measures and has so far registered approximately 33,000 infections. (Photo by Christian Ender/Getty Images).](https://static.sky.it/images/skytg24/it/salute-e-benessere/approfondimenti/covid-indice-rt/19-coronavirus-rt-getty.jpg.transform/gallery-horizontal-mobile/e086944f4f221df38227863831962548fadcf5d3/img.jpg)
Nonostante i limiti, l’indice Rt resta uno dei più solidi indicatori dell’evoluzione della pandemia, che permette meglio di altri di individuarne le fasi
![1277507329 ROME, ITALY - SEPTEMBER 29: People walk in the subway on September 30, 2020 in Rome, Italy. Italy is likely to extend a state of emergency to help keep the coronavirus crisis under control as the government looks to avoid the surge in new cases hitting other European countries. Picture taken September 29, 2020. (Photo by Max Rossi/Getty Images)](https://static.sky.it/images/skytg24/it/salute-e-benessere/approfondimenti/covid-indice-rt/20-coronavirus-rt-getty.jpg.transform/gallery-horizontal-mobile/72e062a27c142f70f23bde34e889ddc0b66a2ffc/img.jpg)
Si può osservare infatti che sebbene il numero di casi attualmente è numericamente simile a quello della fase a cavallo del lockdown, la fase epidemiologica è completamente diversa osservando l'Rt, che resta ben lontano dalla quota 2, raggiunta nelle fasi più critiche