Quarantine
Quarantine is the mandatory restriction of movement and medical observation of asymptomatic individuals, ships, or goods potentially exposed to a contagious pathogen, first codified into law as the thirty-day trentino and forty-day quarantino by the Republic of Ragusa (Dubrovnik) in 1377 and Venice in 1423 during the Second Plague Pandemic.
Quarantine (from the Venetian Italian quarantina or quaranta giorni, meaning "forty days") is a foundational non-pharmaceutical intervention in public health, maritime law, and historical epidemiology that separates and restricts the movement of asymptomatic persons, animals, ships, or merchandise that may have been exposed to a communicable disease until the pathogen's maximum incubation period has elapsed. In strict epidemiological usage, quarantine applies to healthy-appearing contacts or travelers who have potentially been exposed to an infectious agent, whereas isolation refers to the physical separation of symptomatic or laboratory-confirmed infected patients from the susceptible population—and a cordon sanitaire (sanitary cordon) refers to a guarded geographic perimeter blocking travel into or out of an entire plague-stricken city or territory. Born out of the Mediterranean civic response to the Black Death (Yersinia pestis, a zoonotic bacterial pandemic) in 1377 at the Adriatic port of Ragusa (modern Dubrovnik, Croatia) and institutionalized through the construction of the world's first permanent maritime quarantine hospital (lazaretto) by the Republic of Venice on the island of Santa Maria di Nazareth in 1423, quarantine transformed public health from medieval humoral fatalism into a permanent system of state health boards (Magistrati alla Sanità), bills of health (fedi di sanità), and international sanitary treaties—while its modern mathematical effectiveness is governed by the interplay of a pathogen's latent period, incubation period, and pre-symptomatic viral shedding (Grmek, 1980; Cipolla, 1976; Gensini et al., 2004; Fraser et al., 2004).
Historical Archaeology and Legal Origins: From Levitical Isolation to Ragusa (1377) and Venice (1423)
While ancient Mesopotamian tablets (from Mari, ~1780 BCE), the Hebrew Bible (Leviticus 13–14, prescribing a 7-to-14-day priestly inspection and camp exclusion for skin lesions of tzaraath), and seventh-century Umayyad caliphal decrees instituted isolation of visibly ill lepers, none of these early traditions detained healthy-looking travelers or cargo ships on the hypothesis that an invisible contagion could lurk asymptomatically inside a person or bale of cloth.
That conceptual leap occurred during the Second Plague Pandemic following the arrival of Yersinia pestis across the Mediterranean in 1347–1348:
| Date & Civic Polities | Statutory Decree & Architectural Innovation | Archaeological & Public Health Significance |
|---|---|---|
| July 27, 1377 — Republic of Ragusa (Dubrovnik, Croatia) | The Great Council (Maggior Consiglio) of Ragusa enacted the decree Veniens de locis pestiferis non intret Ragusium vel districtum, authored under the guidance of chief municipal physician Jacob of Padua. | World's First Statutory Quarantine (Trentino): Ordered that any ship, merchant, or caravan arriving from a plague-infested region (loca pestifera) could not enter the walled city of Ragusa until spending 30 days (trentina) under open-air observation in the coastal town of Cavtat or on the uninhabited islet of Mrkan, with heavy fines and mandatory confinement for anyone who visited the detainees (Grmek, 1980; Blažina Tomić & Blažina, 2015). |
| 1383–1397 — Marseille & Ragusa Extension to Forty Days (Quarantino) | Ragusa extended the detention period from 30 days (trentino) to 40 days (quarantino), and erected wooden housing and a stone quarantine complex at Danče (1430) and Ploče (1627). | Why 40 days? Historians identify three converging rationales: (1) Hippocratic prognostic doctrine that acute diseases resolve within 40 days (dies critici), (2) the Christian Lenten fast and biblical 40-day purification periods (quadragesima), and (3) empirical observation that 30 days was occasionally insufficient when rat fleas (Xenopsylla cheopis) survived inside grain sacks or wool bales. |
| August 28, 1423 — Republic of Venice (Lazzaretto Vecchio) | The Venetian Senate established the world's first permanent, state-funded maritime isolation and quarantine hospital on the lagoon island of Santa Maria di Nazareth (whose name, conflated with Saint Lazarus, the patron saint of lepers, gave rise to the universal word lazaretto). | Paired in 1468 with a second lagoon island—the Lazzaretto Nuovo—Venice created a two-tier triage architecture: ships with confirmed plague patients or corpses were sent to the Lazzaretto Vecchio (isolation), whereas healthy-appearing crews and cargoes from suspect Levantine ports were sent to the Lazzaretto Nuovo for 40 days of quarantine and cargo airing (sborro). |
| 1485–1630 — Northern Italian Health Magistracies (Magistrati alla Sanità) | Permanent civic Boards of Health established in Venice (1485), Milan (1450/1534), and Florence (1527), armed with sovereign police, judicial, and fiscal powers. | Invented the clean and foul Bill of Health (fede di sanità) signed by port consuls, household plague censuses, mandatory cause-of-death necrologies (Bills of Mortality), and overland cordons sanitaires along the Habsburg–Ottoman military frontier (Militärgrenze, 1710–1871) (Cipolla, 1976; Cliff et al., 2009). |
Bioarchaeology of the Venetian Lazarettos (Lazzaretto Vecchio and Lazzaretto Nuovo)
Modern archaeological excavations on the Venetian lagoon islands of Lazzaretto Vecchio (where over 1,500 plague victims from the 14th to 17th centuries were excavated from mass burial trenches between 2004 and 2010) and Lazzaretto Nuovo have yielded a wealth of material and paleogenomic evidence:
- Ancient DNA Recovery of Yersinia pestis: Dental pulp extracted from skeletons in the 14th- to 17th-century mass trenches of Lazzaretto Vecchio yielded authenticated ancient DNA of Yersinia pestis belonging to the post-Black Death European clade, proving that Mediterranean port cities repeatedly suffered either re-introductions along maritime trade routes or persistent Alpine/hinterland rodent reservoirs (Tran et al., 2011; Spyrou et al., 2016).
- The Tezon Grande and Cargo Fumigation (Sborro): On Lazzaretto Nuovo, Venice constructed the Tezon Grande (1568)—a 102-meter-long open-arched brick warehouse (the largest public building in Venice after the Arsenale ropewalk)—where bastazi porters unpacked bales of Ottoman silk, wool, cotton, and carpets and turned them daily by hand for 40 days while fumigating them with burning rosemary, juniper, sulfur, pitch, and vinegar (which inadvertently killed or drove off infected rat fleas), while detained sailors left hundreds of dated charcoal ship graffiti, merchant seals, and Ottoman/Venetian inscriptions on the interior plaster walls.
From the International Sanitary Conferences (1851) to the WHO International Health Regulations
During the nineteenth century, the explosive expansion of steamships, railways, and the Suez Canal (1869) collided with six global cholera pandemics (Vibrio cholerae) and yellow fever outbreaks. Because arbitrary 40-day port quarantines crippled international commerce while failing to stop waterborne cholera when ships discharged bilge water directly into harbor estuaries, France convened the First International Sanitary Conference in Paris on July 23, 1851.
Over fourteen International Sanitary Conferences between 1851 and 1938—initially deadlocked between "contagionists" (who favored strict Mediterranean-style maritime quarantines) and "anticontagionists / sanitationists" (who argued that filth and miasma caused epidemics and that urban water chlorination and sewers should replace border blockades)—physicians Filippo Pacini (1854), John Snow (1854), Robert Koch (1883), Paul-Louis Simond (1898), and Walter Reed (1900) identified the specific microbial agents, vectors, and exact biological incubation periods of the major epidemic diseases:
- 1892 Venice & 1903 Paris Sanitary Conventions: Replaced arbitrary 40-day detention with pathogen-specific scientific quarantine durations calibrated to the upper 95th–99th percentile of each pathogen's biological incubation period: 5 days for cholera, 6 days for yellow fever (combined with mosquito netting and ship fumigation), and 5 to 10 days for plague (combined with ship deratting via sulfur dioxide or hydrogen cyanide gas).
- WHO International Health Regulations (IHR 1969, revised 2005): Following the foundation of the World Health Organization (WHO) in 1948 and the 2003 SARS-CoV-1 outbreak, the IHR (2005) legally bound 196 state parties to report any Public Health Emergency of International Concern (PHEIC) within 24 hours while requiring that travel and quarantine measures be grounded in scientific risk assessment and proportional to human rights (Upshur, 2002; Cetron & Landwirth, 2005).
Mathematical Theory of Quarantine: Latent Period (Tlat) vs. Incubation Period (Tinc)
Why did classical quarantine and symptom-based contact tracing rapidly extinguish the 2003 SARS-CoV-1 outbreak (~8,096 cases worldwide) and contain Ebola virus outbreaks, yet struggle to halt 1918 H1N1 influenza or 2020 SARS-CoV-2 without population-wide testing or vaccination?
In a landmark 2004 Proceedings of the National Academy of Sciences paper ("Factors that make an infectious disease outbreak controllable"), Christophe Fraser, Steven Riley, Roy M. Anderson, and Neil M. Ferguson proved that the controllability of an epidemic by isolation and contact quarantine depends not only on the basic reproduction number (R0), but on a second critical dimensionless parameter—θ, the proportion of total transmission that occurs prior to symptom onset (or via asymptomatic infections):
where εI is the efficacy/coverage of isolating symptomatic cases upon symptom onset, εT is the fraction of their contacts successfully traced and quarantined before those contacts become infectious, and θ is governed by the relative alignment of two biological clocks inside the infected host:
- The Incubation Period (Tinc): The time from initial infection to the onset of clinical symptoms (fever, cough, rash).
- The Latent Period (Tlat): The time from initial infection to the onset of infectiousness (viral/bacterial shedding).
| Epidemiological Regime | Relative Timing of Tlat vs. Tinc | Pre-Symptomatic Transmission Fraction (θ) | Exemplary Human Pathogens | Controllability by Symptom Isolation & Contact Quarantine |
|---|---|---|---|---|
| Regime I — Infectiousness Follows Symptom Onset (Tlat ≥ Tinc) | Host develops fever or rash before or simultaneously with peak pathogen shedding | θ < 1% to 11% | SARS-CoV-1 (θ < 0.11, R0 ≈ 2.5; peak shedding at day 7–10 of illness), Smallpox (Variola major) (θ < 0.10, R0 ≈ 4–6), Ebola virus (θ ≈ 0, R0 ≈ 1.8) | Highly Controllable: Even moderate symptom isolation (εI ≈ 70%) plus forward contact quarantine (εT ≈ 50%) drives Reff < 1 without requiring mass lockdowns. |
| Regime II — Pre-Symptomatic Shedding Window (Tlat < Tinc) | Pathogen replicates and sheds from upper respiratory mucosa 1 to 3 days before symptoms appear | θ ≈ 30% to 55% | Influenza A (θ ≈ 0.30–0.50, Tinc ≈ 2 d), SARS-CoV-2 (θ ≈ 0.44–0.55; Tlat ≈ 3 d vs. Tinc ≈ 5 d; He et al., 2020) | Requires Rapid Quarantine + Molecular Testing: Symptom isolation alone (εT = 0) leaves Reff ≥ θ R0; control requires ultra-fast contact quarantine within <24 hours, serial RT-PCR/antigen testing to exit quarantine ("test-to-release"), or vaccination. |
| Regime III — Long Asymptomatic Latency (Tlat ≪ Tinc) | Years of silent infectiousness before clinical disease | θ > 80% | HIV-1 (Tinc ≈ 8–10 years to AIDS), Hepatitis C, Syphilis | Quarantine Infeasible: Controlled instead by routine serological/nucleic-acid screening, antiretroviral therapy (U=U, Undetectable = Untransmittable), and barrier prophylaxis. |
References
- Cipolla, C. M. (1976). Public Health and the Medical Profession in the Renaissance. Cambridge University Press. https://www.cambridge.org/9780521209595
- Grmek, M. D. (1980). Le concept d'infection dans l'Antiquité et au Moyen Âge, les anciennes mesures sociales contre les maladies contagieuses et la fondation de la première quarantaine à Dubrovnik (1377). Rad Jugoslavenske akademije znanosti i umjetnosti, 384, 9–54.
- Gensini, G. F., Yacoub, M. H., & Conti, A. A. (2004). The concept of quarantine in history: From plague to SARS. Journal of Infection, 49(4), 257–261. https://doi.org/10.1016/j.jinf.2004.03.002
- Fraser, C., Riley, S., Anderson, R. M., & Ferguson, N. M. (2004). Factors that make an infectious disease outbreak controllable. Proceedings of the National Academy of Sciences, 101(16), 6146–6151. https://doi.org/10.1073/pnas.0307506101
- Tran, T.-N.-N., Signoli, M., Fozzati, L., Aboudharam, G., Raoult, D., & Drancourt, M. (2011). High throughput, multiplexed pathogen detection authenticates plague waves in medieval Venice, Italy. PLOS ONE, 6(3), e16735. https://doi.org/10.1371/journal.pone.0016735
- Blažina Tomić, Z., & Blažina, V. (2015). Expelling the Plague: The Health Office and the Implementation of Quarantine in Dubrovnik, 1377–1533. McGill-Queen's University Press. https://www.mqup.ca/expelling-the-plague-products-9780773545397.php
- He, X., Lau, E. H. Y., Wu, P., Deng, X., Wang, J., Hao, X., Lau, Y. C., Wong, J. Y., Guan, Y., Tan, X., Mo, X., Chen, Y., Liao, B., Chen, W., Hu, F., Zhang, Q., Zhong, M., Wu, Y., Zhao, L., … Leung, G. M. (2020). Temporal dynamics in viral shedding and transmissibility of COVID-19. Nature Medicine, 26(5), 672–675. https://doi.org/10.1038/s41591-020-0869-5