In the spring, about two weeks into the coronavirus lockdown, I found myself thinking about cholera. More specifically, about the 1994 epidemic that killed tens of thousands of Rwandans in Goma, in the east of what was then called Zaire. Initially confined to my home, for me the corona pandemic signified absence: no contact with other people, no travel, no access to the sick and dying. In Goma, by contrast, you could not escape the disease. The sick collapsed in the street or on the fields of sharp black volcanic rock that surrounded the town. They died where they fell. Bodies lay unburied, covered by a blanket or wrapped in rush matting. If you weren’t careful, you might trip over them.

I remembered walking into a tent erected by one of the aid agencies to see dozens of people sprawled semi-conscious on the ground, their eyes glassy, some drooling thick white saliva, family members sitting next to them, cradling their heads. A lone doctor stood in the middle, crying.

‘They’re just dying and dying,’ she sobbed. ‘What can I do?’

The symptoms of cholera are easy to detect: white watery stools and vomit, leading to such a rapid loss of fluids that the eyes begin to sink into the skull and the teeth protrude. Untreated, cholera can cause death in twelve hours, although it’s easily cured by rehydration, administered either orally or intravenously. But the doctor had no drips left, or any oral rehydration salts, or – even more critically – a regular supply of clean water. I began to cry too, as we stood together watching people die.

Through my tears, however, I was aware of an uncomfortable reality: the people dying had, not long before, been killing. They were Hutus, Rwanda’s majority ethnic group. That April, following the shooting down of a plane carrying the Rwandan president, also a Hutu, their leaders had instructed them to kill their neighbours from the minority Tutsi ethnic group. Lawyers do not accept the idea of a collective crime, but a large proportion of the Hutu population, both men and women, played some part in the genocide, even if only by failing to protect the victims, or turning a blind eye to the killing. In villages and towns across Rwanda, the ideology of ‘Hutu Power’ – code for exterminating the Tutsis – took hold, and people who had never committed crimes before were mobilised to murder. I had seen something of the genocide myself, as I had been living in the Rwandan capital, Kigali, when it started. Watching cholera take hold in Goma, I was assailed by the violent images I had seen a few weeks earlier: truckloads of people slashed by machetes or beaten with nail-studded clubs arriving at hospital, drunken men armed with broken beer bottles waving me through roadblocks, flies buzzing over four women with their throats slit outside a clinic.

The Hutus in Goma were generally referred to as refugees, but were they in fact fugitives?

An army of Tutsi exiles, the Rwandan Patriotic Front (RPF), had entered Rwanda from neighbouring countries and vanquished the Hutu army and death squads that had spearheaded the slaughter. Defeated, and fearing revenge killings, the Hutu leaders ordered their people to leave the places where they had committed acts of mass murder and follow them across the border into Zaire. How many of the people who were now dying were soldiers who had thrown off their uniforms? Or members of the notorious militia, the Interahamwe? Or bourgmestres, village mayors, who had orchestrated genocide in the areas they governed? Or were they just obedient souls who had followed orders, wielding agricultural implements as weapons? Now that cholera had struck, they were in the liminal and unrecognised category of both perpetrator and victim.

It was hard not to wonder if the disease was a kind of divine retribution – collective punishment for a collective crime. When this unmodern thought drifted across my mind I tried to dismiss it. It was not, after all, how I looked at the world. But it wouldn’t go away.

There were a lot of large round numbers in those days. It was said that ‘a million’ people had been killed in the genocide. Similarly, it was said that on 14 July, ‘a million’ people were queueing to cross the petite barrière between the Rwandan town of Gisenyi on one side and Goma, in Zaire, on the other. When I arrived two days later, hundreds of thousands of people were still surging through. Some of the women wore kitenge, the brightly coloured cloth Rwandan women use as a wrap, but many others were in rags and barefoot. Normally you would expect noise from such a huge crowd but these people moved silently, pushing chukudus, low long-bodied bicycles with wooden wheels, laden with clothes and aluminium cooking pots. At first the Zairean border guards had attempted to disarm the Hutus; mountains of machetes and hoes and smaller piles of AK-47s and other weapons lay next to the border post. But the guards soon gave up trying to seize weapons, let alone slow or stop the influx.

Goma was a small town then, built by Belgian colonialists on the northern shore of Lake Kivu, in the shadow of a volcanic mountain range that included the Virunga National Park, famous for its mountain gorillas. The jagged black rock that covers the land around Goma is hardened lava from centuries of eruptions. The lava lake in the most active volcano, Nyiragongo, is among the largest in the world. Aerial views show an almost perfect circle of thick, turbulent, boiling liquid with steam rising from the sides. In Rwandan mythology, Nyiragongo consumes the souls of the damned in its fiery cauldron. The day before the refugees started to arrive, the volcano had belched, sending plumes of hissing steam into the atmosphere, a reminder of Nyiragongo’s physical and mystical power.

If you turned left after crossing the border, you soon found yourself in the town’s fancy district where European coffee farmers, business people and Zairean government officials lived in lakeside villas. Any glory had long since passed – the modest colonial-style low-rises were gently crumbling into disrepair – but despite regular power cuts and water shortages the inhabitants still demanded certain standards of their neighbours. Refugees who tried to set up camp there, disturbing the view of the lake, were swiftly shooed away. Most of the Rwandans plodded straight up the single main street with its dilapidated shopfronts, whitewashed walls grown mouldy in the tropical humidity, past street pedlars selling chewing gum and single cigarettes. They moved en masse towards the traffic circle, from which they could head north towards the airport or out into the bush. Neither of these options was tempting. So hard was the rock, it was impossible to knock in a stake or a stick, or anything from which you could hang a piece of cloth for a shelter from the beating sun. In those first few days, many refugees just slept by the border or in town at the side of the road.

I made notes in a slim school exercise book that I had bought in Kigali. During lockdown, I dug it out of the box where it has remained, unread, for the past quarter-century. The faded blue cover is still smeared with mud. My notes start in almost full sentences.

Just by border one man dead amongst piles of belongings. Another lay a few yards away, next to a naked baby and a man in military uniform. An old ragged man in a woolly hat was going through the belongings, searching the pockets of an abandoned coat.

After that, I jotted down fragments of observation and interview, in English and French.

Piles of machetes and hoes.

‘Il y a des bandits.’

Little girl in dirty kitenge, tears on her cheeks.

‘I don’t think I will find my children again.’

3 heaps of weapons at the traffic circle.

Opposite bodies – 5 children sitting alone and hopeless. Silent. Little girl, eyes closed, thin purple cardigan. Bundle of red cloth – another child.

100 yds of weapons.

Mountains of G3s, Belgian, SA and Chinese. Machine guns. Large automatic. Machine mounted, 2 baby goats sleeping underneath.

My memories are fragmented too; piecing them together was my task during the weeks of coronavirus isolation.

One of the key quests in epidemiology is to find Patient Zero, the first person to contract a disease. In the 1854 cholera outbreak in London it was the baby daughter of Sarah and Thomas Lewis. The London epidemic became famous because it led the physician John Snow to map the incidence of the disease. At the time, it was believed that cholera was spread by ‘miasma’, foul-smelling airborne particles, but Snow’s map showed that the epidemic centred on the well and water pump in Broad Street, just next to a leaking cesspool where days before Mr and Mrs Lewis had cast their sick daughter’s soiled nappy. Snow saw the connection, and became convinced that cholera was waterborne, a conclusion that was backed up by the Italian scientist Filippo Pacini, who, the same year, looked through a microscope and saw a comma-shaped bacillus in the intestines of patients who had died of cholera in Florence. Three decades went by before this understanding of cholera’s source and method of transmission was accepted, by which time both Snow and Pacini were dead.

In the Goma epidemic, 140 years later, the name of Patient Zero is lost, if it was ever known. Records say that a team from Médecins Sans Frontières found the first suspected case on 18 July, four days after the Rwandans started to cross the border. It was confirmed on the 20th. All that the Rwandan refugees knew was that some of their number began to fall sick in town, and others in the fields of black rock outside the city where the Zairean authorities had told them to set up camp. The ground was too hard to dig wells and the tankers could not deliver enough water. Aid agencies had prepared for 50,000 Rwandans crossing the border, not upwards of a million. There was only one solution: the women had to collect water from Lake Kivu. Mugunga and Munigi camps were only five kilometres from the lakeshore, but Kibumba and Katale were more than twenty-five kilometres away. Still, the women walked as far as they needed, each of them carrying three plastic jerrycans, one on her head and one in each hand. They were, of course, unaware of the tiny, comma-shaped bacillus Vibrio cholerae lurking in the shallows, or that the disease it carried was endemic in the area. And even if they had been, what choice did they have?

In poor countries, conflict always brings hunger, disease and hardship in its wake. People die unseen and uncounted, because the hospitals no longer function, or because the vaccination programme has collapsed, or because malnutrition renders them susceptible to tuberculosis or malaria. Deaths from bombs and bullets attract more attention because they’re spectacular. But this time, it was the other way around. The genocide had been largely invisible to outsiders – a million murders were concealed among the quiet folds of green hills that enclose the villages of Rwanda. But the cholera that killed the Hutus in Goma was very spectacular indeed. The disease struck in full view of thousands of onlookers – millions if you count the TV viewers.

That was because most journalists had woken up late to the genocide in Rwanda. Distracted by the first democratic elections in South Africa, and unsure what was really going on in this small, far-off country of which they knew little, editors hesitated. Also it was dangerous. By mid-July, more than three months on, realising their mistake but having missed the worst of the killing, editors sent reporters to Goma instead. A TV executive I interviewed later told me he saw the cholera epidemic as ‘such a straightforward story – a humanitarian tragedy unfolding daily’. It wasn’t straightforward at all, of course. He saw a poor, downtrodden mass of Black People dying of disease and being saved by White People – a version of reality that chimed with his expectations. Others saw a band of genocidal killers protected by a bunch of ignorant do-gooders. The ‘straightforward story’ version prevailed, at least initially. Pictures were broadcast, money was raised, and more aid workers and journalists landed at Goma’s airport, where the runway started to crack under the weight of so many aircraft. Bill Clinton, then US president, who had declined to intervene to stop the genocide, described the cholera around Goma as ‘the world’s worst humanitaran crisis for a generation’, and ordered a large relief effort led by the military. Having failed to save Rwandans who were being murdered, the impetus was to help those who were dying of disease. The fact that these were the wrong Rwandans, the perpetrators rather than the victims of genocide, got lost in the rush.

Every morning aid agency press officers held a briefing full of figures: in my Rwandan child’s school exercise book I noted numbers of cases suspected or confirmed, tonnes of supplies needed and litres of water being trucked, and quoted the admissions that they couldn’t cope.

‘We need one plane every minute bringing in saline solution.’

‘Those camps are like hell on earth – volcanic rock. Even if walk in shoes it’s painful.’

‘There’s bubonic plague further north.’

‘There are queues hundreds of metres long for water.’

‘We’re feeling more and more defeated and desperate.’

After the briefing, I would drive with other journalists out to the camps, where people were building flimsy shacks of grass and bright blue plastic sheeting bearing the legend of the UN refugee agency, UNHCR. We grew used to picking our way through bodies. The smell of corpses and faeces was at times overpowering. Until the aid agencies brought in mechanical diggers that could penetrate the rock to carve out latrines, the refugees relieved themselves in the bushes or at the edges of the camps. Flies lighted on the faeces and then on children’s lips and noses as they played in the dirt. Everything was filthy, enabling the disease to spread inexorably through the population.

In the midst of such horror, people talked about the humble lives they had left behind as some kind of rural idyll, a prelapsarian existence interrupted not by the genocide but by the arrival of the RPF – the Inkotanyi or ‘fierce warriors’ – whom they blamed for all their misfortune. Despite the appalling conditions in which they found themselves, they were clear that no families would go back to Rwanda of their own accord, only if their leaders told them that everyone should return.

‘As a farmer, compared to others I could say I was rich because nothing was missing in my family – I grew coffee and potatoes, I had cows. But now I have nothing.’

‘I had almost 400kg of coffee each season. It was quite enough for me to buy things I couldn’t grow like clothes, soap, salt and hoes.’

‘I had two radios but they were stolen by RPF soldiers.’

‘My parents used to tell me that we would be killed in this war by Inkotanyi. When they talk about Inkotanyi, it means people who kill.’

One day I went to Munigi, where I attempted to interview people as they sat next to the corpses of their relatives lying uncollected on the rock. At the back of a medical tent, where bags of saline solution were suspended from what looked like a washing line, I came across Thérèse Mukaukuranga, who was holding a drip for her husband, Niyitanga. She refused to accept that he had the symptoms of cholera. ‘He’s been very sick from tiredness since we fled our home,’ she said. ‘Then he got dysentery.’ Dysentery can be fatal like cholera, but to her it sounded less desperate. Thérèse was a plump woman, wrapped in a yellow-and-black kitenge, still looking like the middle-class urban professional that she was, very different from the peasant farmers who made up the majority of those around her. We chatted in French about their life back in Kigali, where she and her husband had been civil servants. ‘Nous avons travaillé si dur,’ she told me. ‘We worked so hard. We had bought a house and a car.’ Thérèse said life had been good before the war and she shrugged off all mention of genocide. According to her, it never happened – it was the Tutsi RPF that had attacked the Hutus. I knew that it was possible, even likely, that she and her husband had participated in one way or another – they worked for the government that had ordered the killings, and had left the country as commanded. It was hard to know what to do with that thought as we watched her husband gradually expire under a relentless sun, so I put it in the growing category of things that were too difficult to contemplate.

The next day I returned to find her still there, her husband again weaker.