Spread of infectious diseases via inter-state travel: ‘Well-connected’ Indian metros rank high on risk map

A hazard map of Indian cities, accounting for the potential of spreading infectious diseases from typical outbreak locations through inter-city travel, has placed Delhi, Mumbai, Kolkata, Bengaluru, Hyderabad, Chennai, Ahmedabad, Lucknow, Jhansi, Pune and Jaipur in top positions.

Researchers at Indian Institute of Science Education and Research (IISER), Pune, after studying 446 cities with over one lakh population, have linked the transport modes and its usage frequency to understand the spread of infectious diseases from a host city reporting an outbreak and its spread.

Amreli, Gangtok, Shimla, Kannur, Tezpur, Osmanabad, Jorhat and Junagad remained among the cities that had least hazard at the time of an outbreak.

The researchers made use of air, rail and road transport between these cities to bring out this hazard map for the country and compared them with the spread of Covid-19 cases reported between March and July 2020.

“Suppose there is an infectious disease outbreak in a particular city, this map provides a lead time informing how long the disease will take to travel to other parts of the country. With this information, government agencies can stay prepared and plan travel restrictions accordingly,” said MS Santhanam, professor, Department of Physics at IISER, Pune.

In India, railways account for the bulk of long-distance traffic ferrying about 88 lakh people per day, followed by road – 25 lakh and air – 7.5 lakh. As a result, trains not only are infection carriers but also do so over long distances in a country like India, the researchers said.

“This means that railway operations may have to be restricted from the city reporting a disease outbreak to prevent the further spread to the rest of the country,” added Santhanam.

The IISER scientists concluded that it is not the geographical proximity, which plays the deciding factor in a disease spread. Instead, a metric based on frequency of travel on key travel routes is a better predictor of the risks to cities.

For example, Osmanabad (ranked 435) in Maharashtra may be geographically located closer to Mumbai. But, in the event of an outbreak in Mumbai, due to better air and rail connectivity and the sheer number of travellers, the disease will reach Delhi or Kolkata from Mumbai sooner than Osmanabad.

“That is why, it is the effective distance, which puts certain cities higher on the risk map, and not the geographical distance between them,” said Onkar Sadekar and Mansi Budamagunta, fifth-year BS-MS students and co-authors of the study.

The lead time, that is, the available time before a disease makes an in-road from another city can range between one to three days, especially over routes with multiple mobility options and higher travel frequency.

On the other hand, a lead time of up to 15 days can be available for those towns and cities which are not as well-connected or visitor-friendly, the IISER researchers said. They also pointed out that these estimates can be refined with better quality of transport data, especially for road travel.

The outbreak of Covid-19 last year saw international border closures and nationwide shut downs across the world, including India, with no transport services provided for several months.

The researchers argued that rather than closing all transport services across routes and locations in India, the hazard risk of cities and towns must be assessed for timely initiation of measures towards effective curbing of the disease’s spread.

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