On April 7, the same day Jakarta shuttered its schools and non-essential businesses and told its residents to stay at home, the ferry KM Dorolonda sailed into the port city of Baubau, in South-east Sulawesi province in Indonesia's far east.

On board the 146m-long vessel were 621 passengers readying to disembark in the province's second largest city. It was a journey like many others across Indonesia. State-owned ferries, often packed with people and goods, are lifelines for some of the country's 6,000 or so inhabited islands. The Dorolonda itself regularly plied a 2,400km route calling on seven ports, including Namlea and Ambon in Maluku.

This journey, though, was different.

It has come to symbolise the cost of moving too slowly to curb the coronavirus pandemic in a country as vast and under-resourced as Indonesia. It also shows how transport links have spread the virus, and a clearer picture is only just emerging.

Some of those who arrived on April 7 had boarded in Surabaya in East Java and Makassar in South Sulawesi, but most were from Jakarta, where the trip started - 1,755km to the west as the crow flies - and where the outbreak had been spreading for more than a month. The Dorolonda then left Baubau, stopping at several more ports before reaching Ternate, North Maluku, more than 860km to the north-east, over a week later.

On April 17, a total of 19 crew members tested positive for Covid-19 and were quarantined in Ternate.

So, too, was the Dorolonda.

Barred from taking passengers, it later returned to Jakarta, where it is still moored off Tanjung Priok.

In Baubau, the damage was done.

The Dorolonda's 621 passengers had scattered. Some stayed in the city, but more than two-thirds of the passengers travelled into the countryside or to the capital, Kendari, 220km to the north. Still others landed on the surrounding islands, including those of the Wakatobi district 150km to the east.

Locating, testing and then processing samples collected from the passengers took a month, and it is only now that officials are getting an idea of how many cases have occurred because of that voyage.

On May 13, after the nearest laboratory in Makassar, 330km away, finally churned through the test backlog, news arrived that South-east Sulawesi's known cases of coronavirus would spike. In two days, the cases rose to 183, with most linked to the Dorolonda. President Joko Widodo had barred non-essential travel out of Jakarta on April 24, but by then ferries like the Dorolonda had likely spread the virus to the farthest reaches of the archipelago.

All inter-island ferry services have been suspended until next month.

Dr Pandu Riono, an infectious diseases expert at the University of Indonesia, said data gleaned from Facebook suggests 1.7 million people left the greater Jakarta region between April 5 and May 1.

Dr Laode Rabiulawal, a spokesman for South-east Sulawesi's Covid-19 task force, said Jakarta's lockdown needs to stay in force to buy his province time to contain the outbreak, which now stands at 202 cases. But already there are signs that Jakarta residents are chaffing at the restrictions, which were extended again last week. Images of bustling markets filled with maskless shoppers and busy airports despite the ban on non-essential travel have flooded social media.

Cases of Covid-19 outside Jakarta are growing, but the spike in the number of infections, at least in part, stems from Indonesia's improved ability to find them. The country has taken delivery of high volume polymerase chain reaction (PRC) machines and retooled tuberculosis testing equipment it already had to expand its testing capacity.

During the first three weeks of this month, testing more than doubled to 230,000 since the first cases were detected on March 2.

Back in Baubau, which will begin using such a PCR machine this week, Dr Laode said 30 patients have needed to be hospitalised, overwhelming the 16 beds it had readied for Covid-19 cases. Officials are adding another 26 beds, he added.

In Jakarta, it is the opposite story. Roughly half the beds in the nine hospitals set aside for Covid-19 patients are empty.

"It's good news," said Dr Pandu. "But after Ramadan, all those cases may come back to Jakarta."